James Walton "Jimmy" Roosevelt II (December 23, 1907 – August 13, 1991) was an American businessman, Marine, Activist, and Democratic Party Politician. The oldest son of U.S. President Franklin D. Roosevelt and Eleanor Roosevelt, he received the Navy Cross for extraordinary heroism while serving as a Marine Corps officer during World War II. He served as an official Secretary to the President and in the United States House of Representatives.

His first marriage was to philanthropist Betsey Maria Cushing (1909–1998), the middle daughter of surgeon Harvey Williams Cushing and Katharine Stone Crowell. Betsey's sisters were socialites Barbara "Babe" Cushing (1912–1978) and Mary Benedict "Minnie" Cushing (1906–1978). James and Betsey had two daughters, Sara (born 1932) and Kate (1937), before divorcing in 1940.

James married his nurse Romelle Theresa Schneider (1915-2002) the next year. They had three children, James III (born 1945), Michael Anthony (born 1947), and Anna Eleanor "Anne" (born 1949).

Roosevelt attended the 1924 Democratic National Convention where he served, in his words, as his father's "page and prop". In 1928, he and some Harvard classmates campaigned for Democratic Presidential nominee Al Smith. In 1932, he headed FDR's Massachusetts campaign; he made about two hundred campaign speeches that year. Though FDR lost the Massachusetts Democratic primary (to Smith), he easily carried Massachusetts in the November election. James Roosevelt was viewed as his father's political deputy in Massachusetts, allocating patronage in alliance with Boston mayor James Michael Curley. He was also a delegate from Massachusetts to the Constitutional Convention for the repeal of Prohibition in 1933.

Roosevelt was born in New York City at 123 East 36th Street. He attended the Potomac School and the National Cathedral School in Washington, D.C., and the Groton School in Massachusetts. At Groton, he rowed and played football, and was a prefect in his senior year. After graduation in 1926, he attended Harvard College, where he rowed with the freshman and junior varsity crews. At Harvard he followed family traditions, joining the Signet Society and Hasty Pudding Club, of which both his Father and his maternal granduncle and paternal fifth cousin once removed, U.S. President Theodore Roosevelt, had been members, as well as the Fly Club, which his Father had joined, and Institute of the 1770. He graduated from Harvard in 1930 and was elected permanent treasurer of his class.

After graduation, Roosevelt enrolled in the Boston University School of Law. He also took a sales job with Boston insurance agent Victor De Gerard. Roosevelt was so successful, that within one year, he abandoned his law studies. In 1932 he started his own insurance agency, Roosevelt and Sargent, in partnership with John A. Sargent. As President of Roosevelt & Sargent, he made a substantial fortune (about $500,000, or more than $9 million in 2018 dollars). He resigned from the firm in 1937, when he officially went to work in the White House, but retained his half ownership.

Roosevelt was a close protege of Joseph P. Kennedy Sr.. In 1934, the two journeyed to England to obtain the market in post-prohibition liquor imports. Many of Roosevelt's controversial Business ventures were aided by Kennedy, including his maritime insurance interests, and the National Grain Yeast Corp. affair (1933–35). Treasury Secretary Henry Morgenthau, Jr. threatened to resign unless FDR forced James to leave the latter company, suspected of being a front for bootlegging. James Roosevelt was instrumental in securing Kennedy's appointment as ambassador to the United Kingdom.

In April 1936, Presidential Secretary Louis Howe died. James Roosevelt unofficially assumed Howe's duties. Soon after the 1936 re-election of FDR, James Roosevelt was given a direct commission as a lieutenant colonel in the Marine Corps, which caused public controversy for its obvious political implications. He accompanied his Father to the Inter-American Conference at Buenos Aires in December as a military aide. On January 6, 1937, he was officially appointed "administrative assistant to the President"; on July 1, 1937, he was appointed Secretary to the President. He became White House coordinator for eighteen federal agencies in October 1937.

After leaving the White House in November 1938, Roosevelt moved to Hollywood, California, where he first accepted a job as a $750/week administrative assistant for motion picture Producer Samuel Goldwyn. He was on Goldwyn's payroll until November 1940. In 1939 he set up "Globe Productions", a company to produce short films for penny arcades, but the company was liquidated in 1944 while James was on active duty with the Marine Corps. Roosevelt also produced the film Pot o' Gold and distributed the British film Pastor Hall.

World War II broke out in Europe in September 1939; the following month Roosevelt resigned the lieutenant colonel's commission that he had been given in 1936, and was instead commissioned as a captain in the Marine Corps Reserve. He went on active duty in November 1940.

After Japan's Attack on Pearl Harbor on December 7, 1941, Roosevelt requested assignment to combat duty and was transferred to the Marine Raiders in January 1942, a new Marine Corps commando force, and became second-in-command of the 2nd Raider Battalion under Evans Carlson (Carlson's Raiders) whom Roosevelt knew when Carlson commanded the Marine Detachment at the Warm Springs, Georgia residence of Franklin Roosevelt. Roosevelt's influence helped win presidential backing for the Raiders--influenced by the British Commandos--which were opposed by Marine Corps traditionalists.

During his Hollywood period, Roosevelt became involved with Joseph Schenck, a movie mogul who was later caught participating in a payoff scheme that was intended to buy peace with movie industry labor unions. In 1942, Schenck pleaded guilty to one count of perjury and spent four months in prison before being paroled. In October 1945, Harry S. Truman granted Schenck a presidential pardon, a fact which did not become known to the public until 1947.

Despite occasionally debilitating health problems, Roosevelt served with the 2nd Raiders at Midway as a major in early June 1942 and in the Makin Island raid on August 17–18, 1942, where he and 22 others were awarded the Navy Cross. In October, he was given command of the new 4th Raiders, but during training for an upcoming combat operation he became ill enough to be hospitalized in February 1943. Beginning in August 1943, he served in various staff positions during the rest of the war. He was attached to and landed with the U.S. Army's 165th Regimental Combat Team, 27th infantry Division during the invasion of Makin on November 20–23, and was awarded the Silver Star by the Army. He was promoted to colonel on April 13, 1944. He was released from active duty in August 1945 and was placed on the inactive list in October 1945. That same month he became a Compatriot of the Empire State Society of the Sons of the American Revolution.

On July 21, 1946, Roosevelt became chairman of the California State Democratic Central Committee. He also began making daily radio broadcasts of political commentary. Like his brother Elliott, James Roosevelt was prominent in the movement to draft Dwight Eisenhower as the Democratic candidate for President in 1948. When President Truman was renominated instead, Roosevelt stepped down as state chairman on August 8. He remained a Democratic National Committeeman until 1952.

In 1950, Roosevelt was the Democratic candidate for Governor of California, but lost to Republican incumbent Earl Warren by almost 30% of the votes.

In 1954, Roosevelt was elected U.S. Representative from California's 26th congressional district, a heavily Democratic district. He was re-elected to five additional terms and served from 1955 to 1965, resigning during his sixth term. Roosevelt was one of the first politicians to denounce the tactics of Senator Joseph McCarthy. He was also the only Representative to vote against appropriating funds for the House Un-American Activities Committee.

In 1956, he married Gladys Irene Kitchenmaster Owens (1916–1987), his receptionist, and they adopted a son together named Hall Delano (called "Del") in 1959.

His writings include Affectionately, FDR (with Sidney Shalett, 1959) and My Parents, a Differing View (with Bill Libby, 1976). The latter was written in part as a response to his brother Elliott Roosevelt's book An Untold Story, which told of FDR's marital issues and was fiercely repudiated by the other siblings. He authored the novel A Family Matter (with Sam Toperoff, 1979), and edited The Liberal Papers, published in 1962.

He resigned from Congress in October 1965, 10 months into his sixth term, when President Lyndon B. Johnson appointed him a delegate to the United Nations Educational, Scientific, and Cultural Organization (UNESCO). Roosevelt resigned from UNESCO in December 1966, and retired to become an executive of the Investors Overseas Service (IOS) in Geneva, Switzerland.

He married his fourth wife, Mary Winskill, Teacher to his youngest son "Del," in 1969. They had one daughter, Rebecca Mary, in 1971.

Despite having been a liberal Democrat all of his life, Roosevelt joined Democrats for Nixon and publicly supported President Nixon's 1972 re-election, and also supported Ronald Reagan in 1980 and 1984.

In the 1980s, a non-profit organization established by Roosevelt, the National Committee to Preserve Social Security and Medicare, and its associated political action committee, were investigated by the House Ways and Means Committee for questionable money raising practices, and by the Post Office for mail fraud. By direct mail, Roosevelt's group solicited contributions from elderly persons by claiming that Social Security and Medicare programs were in financial jeopardy. Roosevelt also urged contributors to order their Social Security statements of earnings from his group (these are free from the government.)

Roosevelt died in Newport Beach, California in 1991 of complications arising from a stroke and Parkinson's disease. He was 83 and was the last surviving child of Franklin and Eleanor Roosevelt.