The main foreign policy initiative of Roosevelt's first term was the Good Neighbor Policy, which was a re-evaluation of U.S. policy towards Latin America. The United States had frequently intervened in Latin America following the promulgation of the Monroe Doctrine in 1823, and the United States had occupied several Latin American nations in the Banana Wars that had occurred following the Spanish–American War of 1898. After Roosevelt took office, he withdrew U.S. forces from Haiti and reached new treaties with Cuba and Panama, ended their status as U.S. protectorates. In December 1933, Roosevelt signed the Montevideo Convention on the Rights and Duties of States, renouncing the right to intervene unilaterally in the affairs of Latin American countries. Roosevelt also normalized relations with the Soviet Union, which the United States had refused to recognize since the 1920s. Roosevelt hoped to renegotiate the Russian debt from World War I and open trade relations, but no progress was made on either issue, and "both nations were soon disillusioned by the accord."

Roosevelt grew up in a wealthy family. His father, James Roosevelt I, graduated from Harvard Law School in 1851, but chose not to practice law after receiving an inheritance from his grandfather, James Roosevelt. Roosevelt's father was a prominent Bourbon Democrat who once took Franklin to meet President Grover Cleveland in the White House. Sara was the dominant influence in Franklin's early years. She once declared, "My son Franklin is a Delano, not a Roosevelt at all." James, who was 54 when Franklin was born, was considered by some as a remote father, though biographer James MacGregor Burns indicates James interacted with his son more than was typical at the time. Frequent trips to Europe—he made his first excursion at the age of two and went with his parents every year from the ages of seven to fifteen—helped Roosevelt become conversant in German and French. He learned to ride, shoot, row, and play polo and lawn tennis. He took up golf in his teen years, becoming a skilled long hitter. He learned to sail and when he was 16, his father gave him a sailboat.

Roosevelt was born on January 30, 1882, in the Hudson Valley town of Hyde Park, New York, to businessman James Roosevelt I and his second wife, Sara Ann Delano. Roosevelt's parents, who were sixth cousins, both came from wealthy old New York families, the Roosvelts and the Delanos, respectively. Roosevelt's patrilineal ancestor migrated to New Amsterdam in the 17th century, and the Roosevelts flourished as merchants and landowners. The Delano family progenitor traveled to the New World on the Mayflower, and the Delanos prospered as merchants and shipbuilders in Massachusetts. Franklin had a half-brother, James "Rosy" Roosevelt, from his father's previous marriage.

Roosevelt's father died in 1900, causing great distress for him. The following year, Roosevelt's fifth cousin Theodore Roosevelt became President of the United States. Theodore's vigorous leadership style and reforming zeal made him Franklin's role model and hero. Roosevelt graduated from Harvard in 1903 with an A.B. in history. Roosevelt entered Columbia Law School in 1904, but dropped out in 1907 after passing the New York bar exam. In 1908, he took a job with the prestigious Wall Street firm of Carter Ledyard & Milburn, working in the firm's admiralty law division.

In mid-1902, Franklin began courting his Future wife Eleanor Roosevelt, whom he had been acquainted with as a child. Eleanor and Franklin were fifth cousins, once removed, and Eleanor was a niece of Theodore Roosevelt. They began corresponding with each other after meeting in 1902, and in October 1904, Franklin proposed marriage to Eleanor.

On March 17, 1905, Roosevelt married Eleanor in New York City, despite the fierce resistance of his mother. While she did not dislike Eleanor, Sara Roosevelt was very possessive of her son, believing he was too young for marriage. She attempted to break the engagement several times. Eleanor's uncle, President Theodore Roosevelt, stood in at the wedding for Eleanor's deceased father, Elliott. The young couple moved into Springwood, his family's estate at Hyde Park. The home was owned by Sara Roosevelt until her death in 1941 and was very much her home as well. In addition, Franklin and Sara Roosevelt did the planning and furnishing of a town house Sara had built for the young couple in New York City; Sara had a twin house built alongside for herself. Eleanor never felt at home in the houses at Hyde Park or New York, but she loved the family's vacation home on Campobello Island, which Sara gave to the couple.

Biographer James MacGregor Burns said that young Roosevelt was self-assured and at ease in the upper class. In contrast, Eleanor at the time was shy and disliked social life, and at first stayed at home to raise their several children. Like his father had, Franklin left the raising of the children to his wife, while Eleanor in turn largely relied on hired caregivers to raise the children. Referring to her early experience as a mother, she later stated that she knew "absolutely nothing about handling or feeding a baby." Although Eleanor had an aversion to sexual intercourse and considered it "an ordeal to be endured", she and Franklin had six children. Anna, James, and Elliott were born in 1906, 1907, and 1910, respectively. The couple's second son, Franklin, died in infancy in 1909. Another son, also named Franklin, was born in 1914, and the youngest child, John, was born in 1916.

Roosevelt held little passion for the practice of law, and confided to friends that he planned to eventually enter politics. Despite his admiration for his cousin, Theodore, Franklin inherited his father's affiliation with the Democratic Party. Prior to the 1910 elections, the local Democratic Party recruited Roosevelt to run for a seat in the New York State Assembly. Roosevelt was an attractive recruit for the party because Theodore Roosevelt was still one of the country's most prominent politicians, and a Democratic Roosevelt was good publicity; the candidate could also pay for his own campaign. Roosevelt's campaign for the state assembly ended after the Democratic incumbent, Lewis Stuyvesant Chanler, chose to seek re-election. Rather than putting his political hopes on hold, Roosevelt ran for a seat in the state senate. The senate district, located in Dutchess County, Columbia County, and Putnam County, was strongly Republican. Roosevelt feared that open opposition from Theodore could effectively end his campaign, but Theodore privately encouraged his cousin's candidacy despite their differences in partisan affiliation. Acting as his own campaign manager, Roosevelt traveled throughout the senate district via automobile at a time when many could not afford cars. Due to his aggressive and effective campaign, the Roosevelt name's influence in the Hudson Valley, and the Democratic landslide that year, Roosevelt won the election, surprising almost everyone.

Though legislative sessions rarely lasted more than ten weeks, Roosevelt treated his new position as a full-time career. Taking his seat on January 1, 1911, Roosevelt immediately became the leader of a group of "Insurgents" who opposed the bossism of the Tammany Hall machine that dominated the state Democratic Party. In the 1911 U.S. Senate election, which was determined in a joint session of the New York state legislature, Roosevelt and nineteen other Democrats caused a prolonged deadlock by opposing a series of Tammany-backed candidates. Finally, Tammany threw its backing behind James A. O'Gorman, a highly regarded judge who Roosevelt found acceptable, and O'Gorman won the election in late March. Roosevelt soon became a popular figure among New York Democrats, though he had not yet become an eloquent speaker. News articles and cartoons began depicting "the second coming of a Roosevelt" that sent "cold shivers down the spine of Tammany".

Roosevelt, again in opposition to Tammany Hall, supported New Jersey Governor Woodrow Wilson's successful bid for the 1912 Democratic nomination, earning an informal designation as an original Wilson man. The election became a three-way contest, as Theodore Roosevelt left the Republican Party to launch a third party campaign against Wilson and sitting Republican President william Howard Taft. Franklin's decision to back Wilson over Theodore Roosevelt in the general election alienated some members of his family, although Theodore himself was not offended. Wilson's victory over the divided Republican Party made him the first Democrat to win a presidential election since 1892. Overcoming a bout with typhoid fever, and due to the help of Journalist Louis McHenry Howe, Roosevelt was re-elected in the 1912 elections. After the elections, he served as chairman of the Agriculture Committee, and his success with farm and labor bills was a precursor to his New Deal policies twenty years later. By this time he had become more consistently progressive, in support of labor and social welfare programs for women and children; cousin Theodore was of some influence on these issues.

Roosevelt's support of Wilson led to his appointment in March 1913 as Assistant Secretary of the Navy, the second-ranking official in the Navy Department after Secretary Josephus Daniels. Roosevelt had a lifelong affection for the Navy—he had already collected almost 10,000 naval books and claimed to have read all but one—and was more ardent than Daniels in supporting a large and efficient naval force. With Wilson's support, Daniels and Roosevelt instituted a merit-based promotion system and made other reforms to extend civilian control over the autonomous departments of the Navy. Roosevelt oversaw the Navy's civilian employees and earned the respect of union Leaders for his fairness in resolving disputes. Not a single strike occurred during his seven-plus years in the office, during which Roosevelt gained experience in labor issues, government management during wartime, naval issues, and Logistics, all valuable areas for Future office.

Following his defeat in the Senate primary, Roosevelt refocused on the Navy Department. World War I broke out in July 1914, with the Central Powers of Germany, Austria-Hungary, and the Ottoman Empire seeking to defeat the Allied Powers of Britain, France, and Russia. Though he remained publicly supportive of Wilson, Roosevelt sympathized with the Preparedness Movement, whose Leaders strongly favored the Allied Powers and called for a military build-up. The Wilson administration initiated an expansion of the Navy after the sinking of the RMS Lusitania by a German submarine, and Roosevelt helped establish the United States Navy Reserve and the Council of National Defense. In April 1917, after Germany declared it would engage in unrestricted submarine warfare and attacked several U.S. ships, Wilson asked Congress for a declaration of war. Congress approved the declaration of war on Germany on April 6.

Roosevelt requested that he be allowed to serve as a naval officer, but Wilson insisted that he continue to serve as Assistant Secretary of the Navy. For the next year, Roosevelt remained in Washington to coordinate the mobilization, supply, and deployment of naval vessels and personnel. In the first six months after the U.S. entered the war, the Navy expanded fourfold. In the summer of 1918, Roosevelt traveled to Europe to inspect naval installations and meet with French and British officials. In September, he returned to the US on board the USS Leviathan, a large troop carrier. On the 11-day voyage, the pandemic influenza virus struck and killed many on board. Roosevelt became very ill with influenza and a complicating pneumonia. He had recovered by the time the ship landed in New York After Germany signed an armistice in November 1918, surrendering and ending the fighting, Daniels and Roosevelt supervised the demobilization of the Navy. Against the advice of older officers such as Admiral william Benson—who claimed he could not "conceive of any use the fleet will ever have for aviation"—Roosevelt personally ordered the preservation of the Navy's Aviation Division. With the Wilson administration coming to an end, Roosevelt began planning for his next run for office. Roosevelt and his associates approached Herbert Hoover about running for the 1920 Democratic presidential nomination, with Roosevelt as his running mate.

Upon taking office, Roosevelt proposed the construction of a series of hydroelectric power plants and sought to address the ongoing farm crisis of the 1920s. Relations between Roosevelt and Smith suffered after Roosevelt chose not to retain key Smith appointees like Robert Moses. Roosevelt and Eleanor established a political understanding that would last for the duration of his political career; she would dutifully serve as the governor's wife but would also be free to pursue her own agenda and interests. He also began holding "fireside chats", in which he directly addressed his constituents via the radio, often using these chats to pressure the New York State Legislature to advance his agenda. Months into his tenure, the Wall Street Crash of 1929 occurred, and the country began sliding into the Great Depression. While President Hoover and many state governors believed that the economic crisis would subside, Roosevelt saw the seriousness of the situation and established a state employment commission. He also became the first governor to publicly endorse the idea of unemployment insurance.

After the election, Roosevelt returned to New York City, where he practiced law and served as a vice President of the Fidelity and Deposit Company. He also sought to build support for a political comeback in the 1922 elections, but his career was derailed by illness. While the Roosevelts were vacationing at Campobello Island in August 1921, Roosevelt fell ill. His main symptoms were fever; symmetric, ascending paralysis; facial paralysis; bowel and bladder dysfunction; numbness and hyperesthesia; and a descending pattern of recovery. Roosevelt was left permanently paralyzed from the waist down. He was diagnosed with Poliomyelitis at the time, but his symptoms are more consistent with Guillain–Barré syndrome – an autoimmune neuropathy which Roosevelt's doctors failed to consider as a diagnostic possibility.

In 1925, Smith appointed Roosevelt to the Taconic State Park Commission, and his fellow commissioners chose him as chairman. In this role, he came into conflict with Robert Moses, a Smith protégé, who was the primary force behind the Long Island State Park Commission and the New York State Council of Parks. Roosevelt accused Moses of using the name recognition of prominent individuals including Roosevelt to win political support for state parks, but then diverting funds to the ones Moses favored on Long Island, while Moses worked to block the appointment of Howe to a salaried position as the Taconic commission's secretary. Roosevelt served on the commission until the end of 1928, and his contentious relationship with Moses continued as their careers progressed.

As the Democratic Party presidential nominee in the 1928 election, Smith in turn asked Roosevelt to run for governor in the state election. Roosevelt initially resisted the entreaties of Smith and others within the party, as he was reluctant to leave Warm Springs and feared a Republican landslide in 1928. He agreed to run when party Leaders convinced him that only he could defeat the Republican gubernatorial nominee, New York Attorney General Albert Ottinger. Roosevelt won the party's gubernatorial nomination by acclamation, and he once again turned to Louis Howe to lead his campaign. Roosevelt was also joined on the campaign trail by Samuel Rosenman, Frances Perkins, and James Farley, all of whom would become important political associates. While Smith lost the presidency in a landslide, and was defeated in his home state, Roosevelt was elected governor by a one-percent margin. Roosevelt's election as governor of the most populous state immediately made him a contender in the next presidential election.

Roosevelt was viewed as a hero by many African Americans, Catholics, and Jews, and he was highly successful in attracting large majorities of these voters into his New Deal coalition. He won strong support from Chinese Americans and Filipino Americans, but not Japanese Americans, as he presided over their internment in concentration camps during the war. African Americans and Native Americans fared well in two New Deal relief programs, the Civilian Conservation Corps and the Indian Reorganization Act, respectively. Sitkoff reports that the WPA "provided an economic floor for the whole black community in the 1930s, rivaling both agriculture and domestic Service as the chief source" of income.

After the German invasion of Poland, the primary concern of both Roosevelt and his top military staff was on the war in Europe, but Japan also presented foreign policy challenges. Relations with Japan had continually deteriorated since its invasion of Manchuria in 1931, and they had further worsened with Roosevelt's support of China in the Second Sino-Japanese War. With the war in Europe occupying the attention of the major colonial powers, Japanese Leaders eyed vulnerable colonies such as the Dutch East Indies, French Indochina, and British Malaya. After Roosevelt announced a $100 million loan to China in reaction to Japan's occupation of northern French Indochina, Japan signed the Tripartite Pact with Germany and Italy. The pact bound each country to defend the other against attack, and Germany, Japan, and Italy became known as the Axis powers. Overcoming those who favored invading the Soviet Union, the Japanese Army high command successfully advocated for the conquest of Southeast Asia to ensure continued access to raw materials. In July 1941, after Japan occupied the remainder of French Indochina, Roosevelt cut off the sale of oil to Japan, depriving Japan of more than 95 percent of its oil supply. He also placed the Philippine military under American command and reinstated General Douglas MacArthur into active duty to command U.S. forces on the Philippines.

Government spending increased from 8.0% of gross national product (GNP) under Hoover in 1932 to 10.2% of the GNP in 1936. The national debt as a percentage of the GNP had more than doubled under Hoover from 16% to 40% of the GNP in early 1933. It held steady at close to 40% as late as fall 1941, then grew rapidly during the war. The GNP was 34% higher in 1936 than in 1932 and 58% higher in 1940 on the eve of war. That is, the economy grew 58% from 1932 to 1940 in 8 years of peacetime, and then grew 56% from 1940 to 1945 in 5 years of wartime. Unemployment fell dramatically during Roosevelt's first term. It increased in 1938 ("a depression within a depression") but continually declined after 1938. Total employment during Roosevelt's term expanded by 18.31 million jobs, with an average annual increase in jobs during his administration of 5.3%.

While the First New Deal of 1933 had broad support from most sectors, the Second New Deal challenged the Business community. Conservative Democrats, led by Al Smith, fought back with the American Liberty League, savagely attacking Roosevelt and equating him with Karl Marx and Vladimir Lenin. But Smith overplayed his hand, and his boisterous rhetoric let Roosevelt isolate his opponents and identify them with the wealthy vested interests that opposed the New Deal, strengthening Roosevelt for the 1936 landslide. By contrast, labor unions, energized by the Wagner Act, signed up millions of new members and became a major backer of Roosevelt's reelections in 1936, 1940 and 1944.

Roosevelt expected that his party would lose several races in the 1934 Congressional elections, as the president's party had done in most previous midterm elections, but the Democrats picked up seats in both houses of Congress. Empowered by the public's apparent vote of confidence in his administration, the first item on Roosevelt's agenda in the 74th Congress was the creation of a social insurance program. The Social Security Act established Social Security and promised economic security for the elderly, the poor and the sick. Roosevelt insisted that it should be funded by payroll taxes rather than from the general fund, saying, "We put those payroll contributions there so as to give the contributors a legal, moral, and political right to collect their pensions and unemployment benefits. With those taxes in there, no damn Politician can ever scrap my social security program." Compared with the social security systems in western European countries, the Social Security Act of 1935 was rather conservative. But for the first time the federal government took responsibility for the economic security of the aged, the temporarily unemployed, dependent children, and the handicapped. Against Roosevelt's original intention for universal coverage, the act only applied to roughly sixty percent of the labor force, as farmers, domestic workers, and other groups were excluded.

In the 1936 presidential election against Republican Alf Landon and a third party candidate, Roosevelt won 60.8% of the vote and carried every state except Maine and Vermont. The Democratic ticket won the highest proportion of the popular vote. Democrats also expanded their majorities in Congress, winning control of over three-quarters of the seats in each house. The election also saw the consolidation of the New Deal coalition; while the Democrats lost some of their traditional allies in big Business, they were replaced by groups such as organized labor and African Americans, the latter of whom voted Democratic for the first time since the Civil War. Roosevelt lost high income voters, especially businessmen and professionals, but made major gains among the poor and minorities. He won 86 percent of the Jewish vote, 81 percent of Catholics, 80 percent of union members, 76 percent of Southerners, 76 percent of Blacks in northern cities, and 75 percent of people on relief. Roosevelt carried 102 of the nation's 106 cities with a population of 100,000 or more.

With Roosevelt's influence on the wane following the failure of the Judicial Procedures Reform Bill of 1937, conservative Democrats joined with Republicans to block the implementation of further New Deal programs. Roosevelt did manage to pass some legislation, including the Housing Act of 1937, a second Agricultural Adjustment Act, and the Fair Labor Standards Act (FLSA) of 1938, which was the last major piece of New Deal legislation. The FLSA outlawed child labor, established a federal minimum wage, and required overtime pay for certain employees who work in excess of forty-hours per week. He also won passage of the Reorganization Act of 1939 and subsequently created the Executive Office of the President, making it "the nerve center of the federal administrative system." When the economy began to deteriorate again in late 1937, Roosevelt asked Congress for $5 billion in relief and public works funding. This managed to eventually create as many as 3.3 million WPA jobs by 1938. Projects accomplished under the WPA ranged from new federal courthouses and post offices, to facilities and infrastructure for national parks, bridges and other infrastructure across the country, and architectural surveys and archaeological excavations — Investments to construct facilities and preserve important resources. Beyond this, however, Roosevelt recommended to a special congressional session only a permanent national farm act, administrative reorganization, and regional planning measures, all of which were leftovers from a regular session. According to Burns, this attempt illustrated Roosevelt's inability to decide on a basic economic program.

After Kristallnacht in 1938, Roosevelt helped expedite Jewish immigration from Germany and allowed Austrian and German citizens already in the United States to stay indefinitely. He was prevented from accepting more Jewish immigrants by the restrictive Immigration Act of 1924, the prevalence of nativism and antisemitism among voters and members of Congress, and some resistance in the American Jewish community to the acceptance of Eastern European Jewish immigrants. Hitler chose to implement the "Final Solution"–the extermination of the European Jewish population–by January 1942, and American officials learned of the scale of the Nazi extermination campaign in the following months. Against the objections of the State Department, Roosevelt convinced the other Allied Leaders to jointly issue the Joint Declaration by Members of the United Nations, which condemned the ongoing Holocaust and promised to try its perpetrators as war Criminals. In January 1944, Roosevelt established the War Refugee Board to aid Jews and other victims of Axis atrocities. Aside from these actions, Roosevelt believed that the best way to help the persecuted populations of Europe was to end the war as quickly as possible. Top military Leaders and War Department Leaders rejected any campaign to bomb the extermination camps or the rail lines leading to the camps, fearing it would be a diversion from the war effort. According to biographer Jean Edward Smith, there is no evidence that anyone ever proposed such a campaign to Roosevelt himself.

In August 1939, Leo Szilard and Albert Einstein sent the Einstein–Szilárd letter to Roosevelt, warning of the possibility of a German project to develop nuclear weapons. Szilard realized that the recently discovered process of nuclear fission could be used to create a nuclear chain reaction that could be used as a weapon of mass destruction. Roosevelt feared the consequences of allowing Germany to have sole possession of the Technology, and authorized preliminary research into nuclear weapons. After the attack on Pearl Harbor, the Roosevelt administration secured the funds needed to continue research and selected General Leslie Groves to oversee the Manhattan Project, which was charged with developing the first nuclear weapons. Roosevelt and Churchill agreed to jointly pursue the project, and Roosevelt helped ensure that American Scientists cooperated with their British counterparts.

While some Democrats had opposed Roosevelt's nomination in 1940, the President faced little difficulty in securing his re-nomination at the 1944 Democratic National Convention. Roosevelt made it clear before the convention that he was seeking another term, and on the lone presidential ballot of the convention Roosevelt won the vast majority of delegates, although a minority of Southern Democrats voted for Harry F. Byrd. Party Leaders prevailed upon Roosevelt to drop Vice President Wallace from the ticket, believing him to be an electoral liability and a poor potential successor in case of Roosevelt's death. Roosevelt preferred Byrnes as Wallace's replacement but was convinced to support Senator Harry S. Truman of Missouri, who had earned renown for his investigation of war production inefficiency and was acceptable to the various factions of the party. On the second vice presidential ballot of the convention, Truman defeated Wallace to win the nomination.

Roosevelt did not join NAACP Leaders in pushing for federal anti-lynching legislation, as he believed that such legislation was unlikely to pass and that his support for it would alienate Southern congressmen. He did, however, appoint a "Black Cabinet" of African American advisers to advise on race relations and African American issues, and he publicly denounced lynching as "murder." First Lady Eleanor Roosevelt vocally supported efforts designed to aid the African American community, including the Fair Labor Standards Act, which helped boost wages for nonwhite workers in the South. In 1941, Roosevelt established the Fair Employment Practices Committee (FEPC) to implement Executive Order 8802, which prohibited racial and religious discrimination in employment among defense contractors. The FEPC was the first national program directed against employment discrimination, and it played a major role in opening up new employment opportunities to non-white workers. During World War II, the proportion of African American men employed in Manufacturing positions rose significantly. In response to Roosevelt's policies, African Americans increasingly defected from the Republican Party during the 1930s and 1940s, becoming an important Democratic voting bloc in several Northern states.

The attack on Pearl Harbor raised concerns in the public regarding the possibility of sabotage by Japanese Americans. This suspicion was fed by long-standing racism against Japanese immigrants, as well as the findings of the Roberts Commission, which concluded that the attack on Pearl Harbor had been assisted by Japanese spies. On February 19, 1942, President Roosevelt signed Executive Order 9066, which relocated hundreds of thousands of the Japanese-American citizens and immigrants. They were forced to liquidate their properties and businesses and interned in hastily built camps in interior, harsh locations. Distracted by other issues, Roosevelt had delegated the decision for internment to Secretary of War Stimson, who in turn relied on the judgment of Assistant Secretary of War John J. McCloy. The Supreme Court upheld the constitutionality of the executive order in the 1944 case of Korematsu v. United States. Many German and Italian citizens were also arrested or placed into internment camps.

In late 1943, Roosevelt, Churchill, and Stalin agreed to meet to discuss strategy and post-war plans, and at the Tehran Conference, Roosevelt met with Stalin for the first time. At the conference, Britain and the United States committed to opening a second front against Germany in 1944, while Stalin committed to entering the war against Japan at an unspecified date. Subsequent conferences at Bretton Woods and Dumbarton Oaks established the framework for the post-war international monetary system and the United Nations, an intergovernmental organization similar to Wilson's failed League of Nations.

The Republicans nominated Thomas E. Dewey, the governor of New York who had a reputation as a liberal in his party. The opposition lambasted Roosevelt and his administration for domestic corruption, bureaucratic inefficiency, tolerance of Communism, and military blunders. Labor unions, which had grown rapidly in the war, threw their all-out support behind Roosevelt. Roosevelt and Truman won the 1944 election by a comfortable margin, defeating Dewey and his running mate John W. Bricker with 53.4% of the popular vote and 432 out of the 531 electoral votes. The President campaigned in favor of a strong United Nations, so his victory symbolized support for the nation's Future participation in the international community.

On March 29, 1945, Roosevelt went to the Little White House at Warm Springs, to rest before his anticipated appearance at the founding conference of the United Nations. On the afternoon of April 12, Roosevelt said, "I have a terrific headache." He then slumped forward in his chair, unconscious, and was carried into his bedroom. The president's attending cardiologist, Dr. Howard Bruenn, diagnosed the medical emergency as a massive cerebral hemorrhage. At 3:35 p.m. that day, Roosevelt died at the age of 63. An editorial by The New York Times declared, "Men will thank God on their knees a hundred years from now that Franklin D. Roosevelt was in the White House."

Roosevelt's home in Hyde Park is now a National Historic Site and home to his Presidential library. Washington D.C., hosts two memorials to the former President. The largest, the 7.50-acre Roosevelt Memorial, is located next to the Jefferson Memorial on the Tidal Basin. A much more modest memorial, a block of marble in front of the National Archives building, was erected in 1965. Roosevelt's leadership in the March of Dimes is one reason he is commemorated on the American dime. Roosevelt has also appeared on several U.S. Postage stamps.

The rapid expansion of government programs that occurred during Roosevelt's term redefined the role of the government in the United States, and Roosevelt's advocacy of government social programs was instrumental in redefining liberalism for coming generations. Roosevelt firmly established the United States' leadership role on the world stage, with his role in shaping and financing World War II. His isolationist critics faded away, and even the Republicans joined in his overall policies. He also created a new understanding of the presidency, permanently increasing the power of the President at the expense of Congress. After his death, his widow, Eleanor, continued to be a forceful presence in US and world politics, serving as delegate to the conference which established the United Nations and championing civil rights and liberalism generally. Many members of his administration played leading roles in the administrations of Truman, Kennedy and Johnson, each of whom embraced Roosevelt's political legacy. Reflecting on Roosevelt's presidency, "which brought the United States through the Great Depression and World War II to a prosperous future", said FDR biographer Jean Edward Smith in 2007, "He lifted himself from a wheelchair to lift the nation from its knees."

Roosevelt presided over the establishment of several agencies and measures designed to provide relief for the unemployed and others in need. The Federal Emergency Relief Administration (FERA), under the leadership of Harry Hopkins, was designed to distribute relief to state governments. The Public Works Administration (PWA), under the leadership of Secretary of the Interior Harold Ickes, was created to oversee the construction of large-scale public works such as dams, bridges, and schools. The most popular of all New Deal agencies – and Roosevelt's favorite – was the Civilian Conservation Corps (CCC), which hired 250,000 unemployed young men to work on local rural projects. Roosevelt also expanded a Hoover agency, the Reconstruction Finance Corporation, making it a major source of financing for railroads and industry. Congress gave the Federal Trade Commission broad new regulatory powers and provided mortgage relief to millions of farmers and homeowners. Roosevelt also made agricultural relief a high priority and set up the Agricultural Adjustment Administration (AAA). The AAA tried to force higher prices for commodities by paying farmers to leave land uncultivated and to cut herds.

Roosevelt tried to keep his campaign promise by cutting the federal budget — including a reduction in military spending from $752 million in 1932 to $531 million in 1934 and a 40% cut in spending on veterans benefits — by removing 500,000 veterans and widows from the pension rolls and reducing benefits for the remainder, as well as cutting the salaries of federal employees and reducing spending on research and education. But the veterans were well organized and strongly protested, and most benefits were restored or increased by 1934. Veterans groups such as the American Legion and the Veterans of Foreign Wars won their campaign to transform their benefits from payments due in 1945 to immediate cash when Congress overrode the President's veto and passed the Bonus Act in January 1936. It pumped sums equal to 2% of the GDP into the consumer economy and had a major stimulus effect.