Lyndon Baines Johnson was born on August 27, 1908, near Stonewall, Texas, in a small farmhouse on the Pedernales River. He was the oldest of five children born to Samuel Ealy Johnson Jr. and Rebekah Baines. Johnson had one brother, Sam Houston Johnson, and three sisters; Rebekah, Josefa, and Lucia. The nearby small town of Johnson City, Texas, was named after LBJ's cousin, James Polk Johnson, whose forebears had moved west from Georgia. Johnson had English, German, and Ulster Scots ancestry. His patrilineal descent traces back to John Johnson, born in Dumfriesshire, Scotland in 1590. He was maternally descended from pioneer Baptist clergyman George Washington Baines, who pastored eight churches in Texas, as well as others in Arkansas and Louisiana. Baines, the grandfather of Johnson's mother, was also the President of Baylor University during the American Civil War.

In school, Johnson was an awkward, talkative youth and was elected President of his 11th-grade class. He graduated in 1924 from Johnson City High School, where he participated in public speaking, debate, and baseball. At age 15, Johnson was the youngest member of his class. Pressured by his parents to attend college, he enrolled at a "subcollege" of Southwest Texas State Teachers College (SWTSTC) in the summer of 1924, where students from unaccredited high schools could take the 12th-grade courses needed for admission to college. He left the school just weeks after his arrival, and decided to move to Southern California. He worked at his cousin's legal practice and in various odd jobs before returning to Texas, where he worked as a day laborer.

In 1926, Johnson managed to enroll at SWTSTC (now Texas State University). He worked his way through school, participated in debate and campus politics, and edited the school newspaper, The College Star. The college years refined his skills of persuasion and political organization. For nine months, from 1928 to 1929, Johnson paused his studies to teach Mexican-American children at the segregated Welhausen School in Cotulla, some 90 miles (140 km) south of San Antonio in La Salle County. The job helped him to save money to complete his education, and he graduated in 1930. He briefly taught at Pearsall High School before taking a position as Teacher of public speaking at Sam Houston High School in Houston.

After Richard M. Kleberg won a 1931 special election to represent Texas in the United States House of Representatives, he appointed Johnson as his legislative secretary. Johnson got the position on the recommendation of his own father and that of State Senator Welly Hopkins, who Johnson had campaigned for in 1930. Kleberg had little interest in performing the day-to-day duties of a Congressman, instead delegating them to Johnson. After Franklin D. Roosevelt won the 1932 presidential election, Johnson became a staunch supporter of Roosevelt's New Deal. Johnson was elected speaker of the "Little Congress," a group of Congressional aides, where he cultivated Congressmen, newspapermen, and lobbyists. Johnson's friends soon included aides to President Roosevelt as well as fellow Texans such as Vice President John Nance Garner and Congressman Sam Rayburn.

Johnson married Claudia Alta Taylor, also known as "Lady Bird", of Karnack, Texas on November 17, 1934, after he attended Georgetown University Law Center for several months. The wedding was officiated by Rev. Arthur R. McKinstry at St. Mark's Episcopal Church in San Antonio. They had two daughters, Lynda Bird, born in 1944, and Luci Baines, born in 1947. Johnson gave his children names with the LBJ initials; his dog was Little Beagle Johnson. His was the LBJ Ranch; his initials were on his cufflinks, ashtrays, and clothes.

In 1935, he was appointed head of the Texas National Youth Administration, which enabled him to use the government to create education and job opportunities for young people. He resigned two years later to run for Congress. Johnson, a notoriously tough boss throughout his career, often demanded long workdays and work on weekends. He was described by friends, fellow politicians, and historians as motivated by an exceptional lust for power and control. As Johnson's biographer Robert Caro observes, "Johnson's ambition was uncommon—in the degree to which it was unencumbered by even the slightest excess weight of ideology, of philosophy, of principles, of beliefs."

In 1937, Johnson successfully campaigned in a special election for Texas's 10th congressional district, that covered Austin and the surrounding hill country. He ran on a New Deal platform and was effectively aided by his wife. He served in the House from April 10, 1937, to January 3, 1949. President Franklin D. Roosevelt found Johnson to be a welcome ally and conduit for information, particularly with regard to issues concerning internal politics in Texas (Operation Texas) and the machinations of Vice President John Nance Garner and Speaker of the House Sam Rayburn. Johnson was immediately appointed to the Naval Affairs Committee. He worked for rural electrification and other improvements for his district. Johnson steered the projects towards contractors that he personally knew, such as the Brown Brothers, Herman and George, who would Finance much of Johnson's Future career. In 1941, he ran for the Democratic U.S. Senate nomination in a special election; his main opponent was the sitting Governor of Texas, businessman and radio personality W. Lee O'Daniel; Johnson narrowly lost the Democratic primary, which was then tantamount to election, with O'Daniel receiving 175,590 votes (30.49%), and Johnson 174,279 (30.26%).

Johnson was appointed a Lieutenant Commander in the U.S. Naval Reserve on June 21, 1940. While serving as a U.S. congressman, he was called to active duty three days after the Japanese attack on Pearl Harbor in December 1941. His orders were to report to the Office of the Chief of Naval Operations in Washington, D.C. for instruction and training. Following his training, he asked Undersecretary of the Navy James Forrestal for a combat assignment. He was sent instead to inspect the shipyard facilities in Texas and on the West Coast. In the spring of 1942, President Roosevelt needed his own reports on what conditions were like in the Southwest Pacific. Roosevelt felt that information which flowed up the military chain of command needed to get delivered by a highly trusted political aide. From a suggestion by Forrestal, Roosevelt assigned Johnson to a three-man survey team of the Southwest Pacific.

In addition to the Silver Star, Johnson received the American Campaign Medal, Asiatic-Pacific Campaign Medal, and the World War II Victory Medal. He was released from active duty on July 17, 1942 and remained in the Navy Reserve, later promoted to commander on October 19, 1949 (effective June 2, 1948). He resigned from the Navy Reserve effective January 18, 1964.

In the 1948 elections, Johnson again ran for the Senate and won in a highly controversial result in a three-way Democratic Party primary. Johnson faced a well-known former governor, Coke Stevenson, and George Peddy (a former state representative of District 8 in Shelby County). Johnson drew crowds to fairgrounds with his rented helicopter dubbed "The Johnson City Windmill". He raised money to flood the state with campaign circulars and won over conservatives by voting for the Taft-Hartley act (curbing union power) as well as by criticizing unions. Stevenson came in first but lacked a majority, so a runoff was held; Johnson campaigned even harder, while Stevenson's efforts slumped.

Johnson was appointed to the Senate Armed Services Committee, and later in 1950, he helped create the Preparedness Investigating Subcommittee. Johnson became its chairman and conducted investigations of defense costs and efficiency. These investigations revealed old investigations and demanded actions that were already being taken in part by the Truman Administration, although it can be said that the committee's investigations reinforced the need for changes. Johnson gained headlines and national attention through his handling of the press, the efficiency with which his committee issued new reports, and the fact that he ensured that every report was endorsed unanimously by the committee. Johnson used his political influence in the Senate to receive broadcast licenses from the Federal Communications Commission in his wife's name. After the 1950 general elections, Johnson was chosen as Senate Majority Whip in 1951 under the new Majority Leader, Ernest McFarland of Arizona, and served from 1951 to 1953.

Johnson's Cowboy hat and boots reflected his Texas roots and genuine love of the rural hill country. From 250 acres (100 ha) of land that he was given by an aunt in 1951, he created a 2,700-acre (1,100 ha) working ranch with 400 head of registered Hereford cattle. The National Park Service keeps a herd of Hereford cattle descended from Johnson's registered herd and maintains the ranch property.

In the 1952 general election, Republicans won a majority in both the House and Senate. Among defeated Democrats that year was McFarland, who lost to upstart Barry Goldwater. In January 1953, Johnson was chosen by his fellow Democrats to be the minority leader; he became the most junior Senator ever elected to this position. One of his first actions was to eliminate the seniority system in making appointments to committees, while retaining it for chairmanships. In the 1954 election, Johnson was re-elected to the Senate, and since the Democrats won the majority in the Senate, Johnson then became majority leader. Former majority leader william Knowland became minority leader. Johnson's duties were to schedule legislation and help pass measures favored by the Democrats. Johnson, Rayburn and President Dwight D. Eisenhower worked well together in passing Eisenhower's domestic and foreign agenda.

At Kennedy's death, there were 16,000 American military personnel stationed in Vietnam; these personnel supported South Vietnam in the Vietnam War against North Vietnam. Vietnam had been partitioned at the 1954 Geneva Conference into two countries, with North Vietnam led by a Communist government. Johnson subscribed to the Domino Theory in Vietnam and to a containment policy that required America to make a serious effort to stop all Communist expansion. On taking office, Johnson immediately reversed Kennedy's order to withdraw 1,000 military personnel by the end of 1963. In late summer 1964, Johnson seriously questioned the value of staying in Vietnam but, after meeting with Secretary of State Dean Rusk and Chairman of the Joint Chiefs of Staff Maxwell D. Taylor, declared his readiness "to do more when we had a base" or when Saigon was politically more stable. He expanded the numbers and roles of the American military following the Gulf of Tonkin Incident.

A 60-cigarette-per-day smoker, Johnson suffered a near-fatal heart attack on July 2, 1955. He abruptly gave up smoking as a result, with only a couple of exceptions, and did not resume the habit until he left the White House on January 20, 1969. Johnson announced he would remain as his party's leader in the Senate on New Year's Eve 1955, his doctors reporting he had made "a most satisfactory recovery" since his heart attack five months prior.

Johnson's success in the Senate rendered him a potential Democratic presidential candidate; he had been the "favorite son" candidate of the Texas delegation at the Party's national convention in 1956, and appeared to be in a strong position to run for the 1960 nomination. Jim Rowe repeatedly urged Johnson to launch a campaign in early 1959, but Johnson thought it better to wait, thinking that John Kennedy's efforts would create a division in the ranks which could then be exploited. Rowe finally joined the Humphrey campaign in frustration, another move which Johnson thought played into his own strategy.

During the Suez Crisis, Johnson tried to prevent the US government from criticizing the Israeli invasion of the Sinai peninsula. Along with the rest of the nation, Johnson was appalled by the threat of possible Soviet domination of space FLIGHT implied by the launch of the first artificial Earth satellite Sputnik 1, and used his influence to ensure passage of the 1958 National Aeronautics and Space Act, which established the civilian space agency NASA.

At the same time as his vice presidential run, Johnson also sought a third term in the U.S. Senate. According to Robert Caro, "On November 8, 1960, Lyndon Johnson won election for both the vice presidency of the United States, on the Kennedy-Johnson ticket, and for a third term as senator (he had Texas law changed to allow him to run for both offices). When he won the vice presidency, he made arrangements to resign from the Senate, as he was required to do under federal law, as soon as it convened on January 3, 1961." (In 1988, Lloyd Bentsen, the vice presidential running mate of Democratic presidential candidate Michael Dukakis, and a Senator from Texas, took advantage of "Lyndon's law," and was able to retain his seat in the Senate despite Dukakis' loss to George H. W. Bush.)

Kennedy also appointed Johnson Chairman of the National Aeronautics Space Council. The Soviets beat the US with the first manned spaceflight in April 1961, and Kennedy gave Johnson the task of evaluating the state of the US space program and recommending a project that would allow the US to catch up or beat the Soviets. Johnson responded with a recommendation that the US gain the leadership role by committing the resources to embark on a project to land an American on the Moon in the 1960s. Kennedy assigned priority to the space program, but Johnson's appointment provided potential cover in case of a failure.

Johnson's initial effort to improve Health care was the creation of The Commission on Heart Disease, Cancer and Strokes (HDCS). Combined, these diseases accounted for 71 percent of the nation's deaths in 1962. To enact recommendations of the commission, Johnson asked Congress for funds to set up the Regional Medical Program (RMP), to create a network of hospitals with federally funded research and practice; Congress passed a significantly watered down version.

President Kennedy had submitted a civil-rights bill to Congress in June 1963, which was met with strong opposition. Johnson renewed the effort and asked Bobby Kennedy to spearhead the undertaking for the administration on Capitol Hill. This provided adequate political cover for Johnson should the effort fail; but if it were successful, Johnson would receive ample credit. Historian Robert Caro notes that the bill Kennedy had submitted was facing the same tactics that prevented the passage of civil rights bills in the past; southern congressmen and senators used congressional procedure to prevent it from coming to a vote. In particular, they held up all of the major bills Kennedy had proposed and that were considered urgent, especially the tax reform bill, in order to force the bill's supporters to pull it.

In the winter of 1964–65 Johnson was pressured by the military to begin a bombing campaign to forcefully resist a communist takeover in South Vietnam; moreover, a plurality in the polls at the time were in favor of military action against the communists, with only 26 to 30 percent opposed. Johnson revised his priorities, and a new preference for stronger action came at the end of January with yet another change of government in Saigon. He then agreed with Mac Bundy and McNamara, that the continued passive role would only lead to defeat and withdrawal in humiliation. Johnson said, "Stable government or no stable government in Saigon we will do what we ought to do. I'm prepared to do that; we will move strongly. General Nguyễn Khánh (head of the new government) is our boy".

Johnson anticipated court challenges to his legislative measures in 1965, and thought it advantageous to have a "mole" in the Supreme Court who he thought could provide him with inside information, as he was able to get from the legislative branch. Abe Fortas in particular was the individual that Johnson thought could fill the bill. The opportunity arose when an opening occurred for Ambassador to the UN, with Adlai Stevenson's death; Associate Justice Arthur Goldberg accepted Johnson's offer to transfer to the UN position. Johnson insisted on Fortas assuming Goldberg's seat, over Fortas's wife's objection that it was too early in his career. Mrs. Fortas expressed disapproval to Johnson personally afterwards. When Earl Warren announced his retirement in 1968, Johnson nominated Fortas to succeed him as Chief Justice of the United States, and nominated Homer Thornberry to succeed Fortas as Associate Justice. However, Fortas's nomination was filibustered by senators, and neither nominee was voted upon by the full Senate.

Biographer Randall Woods argues that Social Gospel themes Johnson learned from childhood allowed him to transform social problems into moral problems. This helps explain his longtime commitment to social justice, as exemplified by the Great Society and his commitment to racial equality. The Social Gospel explicitly inspired his foreign-policy approach to a sort of Christian internationalism and nation building. For Example, in a 1966 speech he quoted at length from the Social Creed of the Methodist Church issued in 1940, adding "It would be very hard for me to write a more perfect description of the American ideal."

The Soviet Union supported its Arab allies. In May 1967, the Soviets started a surge deployment of their naval forces into the East Mediterranean. Early in the crisis they began to Shadow the US and British carriers with destroyers and intelligence collecting vessels. The Soviet naval squadron in the Mediterranean was sufficiently strong to act as a major restraint on the U.S. Navy. In a 1983 interview with The Boston Globe, McNamara claimed that "We damn near had war". He said Kosygin was angry that "we had turned around a carrier in the Mediterranean".

After Robert Kennedy's assassination, Johnson rallied the party bosses and unions to give Humphrey the nomination at the 1968 Democratic National Convention. Personal correspondences between the President and some in the Republican Party suggested Johnson tacitly supported Nelson Rockefeller's campaign. He reportedly said that if Rockefeller became the Republican nominee, he would not campaign against him (and would not campaign for Humphrey). In what was termed the October surprise, Johnson announced to the nation on October 31, 1968, that he had ordered a complete cessation of "all air, naval and artillery bombardment of North Vietnam", effective November 1, should the Hanoi Government be willing to negotiate and citing progress with the Paris peace talks. In the end, Democrats did not fully unite behind Humphrey, enabling Republican candidate Richard Nixon to win the election.

After leaving the presidency in January 1969, Johnson went home to his ranch in Stonewall, Texas, accompanied by former aide and speechwriter Harry J. Middleton, who would draft Johnson's first book, The Choices We Face, and work with him on his memoirs entitled The Vantage Point: Perspectives of the Presidency 1963–1969, published in 1971. That year, the Lyndon Baines Johnson Library and Museum opened on the campus of The University of Texas at Austin. He donated his Texas ranch in his will to the public to form the Lyndon B. Johnson National Historical Park, with the provision that the ranch "remain a working ranch and not become a sterile relic of the past".

In March 1970, Johnson suffered an attack of angina and was taken to Brooke Army General Hospital on Fort Sam Houston in San Antonio. He was urged to lose a considerable amount of weight. Johnson had grown dangerously heavier since leaving the White House, gaining more than 25 pounds (11 kg) and weighing around 235 pounds (107 kg). He had also resumed smoking after nearly 15 years without having done so, which contributed further to his health problems. The following summer, again gripped by chest pains, he embarked on a crash water diet, shedding about 15 pounds (6.8 kg) in less than a month. In April 1972, Johnson fell victim to a second heart attack while visiting his daughter, Lynda, in Charlottesville, Virginia. "I'm hurting real bad," he confided to friends. The chest pains hit him nearly every afternoon—a series of sharp, jolting pains that left him scared and breathless. A portable oxygen tank stood next to his bed, and he periodically interrupted what he was doing to lie down and don the mask to gulp air. He continued to smoke heavily, and, although placed on a low-calorie, low-cholesterol diet, kept to it only in fits and starts. Meanwhile, he began experiencing severe abdominal pains. Doctors diagnosed this Problem through X-rays as diverticulosis—pouches of tissue forming on the intestine. His condition rapidly worsened and surgery was recommended, so Johnson flew to Houston to consult with heart specialist Dr. Michael DeBakey. DeBakey discovered that even though two of the former President's coronary arteries were critically damaged, the overall condition of his heart was so poor that even attempting a bypass surgery would likely result in fatal complications.

Shortly after Johnson's death, his press secretary Tom Johnson (no relation) telephoned Walter Cronkite at CBS; Cronkite was live on the air with the CBS Evening News at the time, and a report on Vietnam was cut abruptly while Cronkite was still on the line, so he could break the news. Johnson's death came two days after Richard Nixon's second inauguration, which followed Nixon's landslide victory in the 1972 election. His death meant that for the first time since 1933, when Calvin Coolidge died during Herbert Hoover's final months in office, that there were no former Presidents still living; Johnson had been the only living ex-President since December 26, 1972, following the death of Harry S. Truman. As of 2018, Johnson remains the most recent former Democratic President to die.

With Johnson's heart condition now diagnosed as terminal, he returned home to his ranch outside San Antonio. At approximately 3:39 pm Central Time on January 22, 1973, Johnson suffered a massive heart attack. After he had placed a call to the Secret Service agents on the ranch, they rushed to the former President's bedroom. There, they found Johnson still holding the telephone receiver in his hand, unconscious and not breathing. Johnson was airlifted in one of his own airplanes to San Antonio and taken to Brooke Army General, where he was pronounced dead on arrival at the facility by cardiologist and Army colonel Dr. George McGranahan. He was 64 years old.

The Manned Spacecraft Center in Houston was renamed the Lyndon B. Johnson Space Center in 1973, and Texas created a legal state holiday to be observed on August 27 to mark Johnson's birthday. It is known as Lyndon Baines Johnson Day. The Lyndon Baines Johnson Memorial Grove on the Potomac was dedicated on April 6, 1976.

For the first time, large amounts of federal money went to public schools. In practice ESEA meant helping all public school districts, with more money going to districts that had large proportions of students from poor families (which included all the big cities). For the first time private schools (most of them Catholic schools in the inner cities) received services, such as library funding, comprising about 12 percent of the ESEA budget. Though federal funds were involved, they were administered by local officials, and by 1977 it was reported that less than half of the funds were actually applied toward the education of children under the poverty line. Dallek further reports that researchers cited by Hugh Davis Graham soon found that poverty had more to do with family background and neighborhood conditions than the quantity of education a child received. Early studies suggested initial improvements for poor children helped by ESEA reading and math programs, but later assessments indicated that benefits faded quickly and left pupils little better off than those not in the schemes. Johnson's second major education program was the Higher Education Act of 1965, which focused on funding for lower income students, including grants, work-study money, and government loans.

Johnson was awarded the Presidential Medal of Freedom posthumously in 1980.

In a 1993 interview for the Johnson Presidential Library oral history archives, Johnson's Secretary of Defense Robert McNamara stated that a carrier battle group, the U.S. 6th Fleet, sent on a training exercise toward Gibraltar was re-positioned back towards the eastern Mediterranean to be able to assist Israel during the Six-Day War of June 1967. Given the rapid Israeli advances following their strike on Egypt, the administration "thought the situation was so tense in Israel that perhaps the Syrians, fearing Israel would attack them, or the Soviets supporting the Syrians might wish to redress the balance of power and might attack Israel". The Soviets learned of this course correction and regarded it as an offensive move. In a hotline message from Moscow, Soviet Premier Alexei Kosygin said, "If you want war you're going to get war."

Johnson was buried in his family cemetery (which, although it is part of the Lyndon B. Johnson National Historical Park in Stonewall, Texas, is still privately owned by the Johnson family, who have requested that the public not enter the cemetery), a few yards from the house in which he was born. Eulogies were given by former Texas governor John Connally and the Rev. Billy Graham, the minister who officiated at the burial rites. The state funeral, the last for a President until Ronald Reagan's in 2004, was part of an unexpectedly busy week in Washington, as the Military District of Washington (MDW) dealt with its second major task in less than a week, beginning with Nixon's second inauguration. The inauguration affected the state funeral in various ways, because Johnson died only two days after the inauguration. The MDW and the Armed Forces Inaugural Committee canceled the remainder of the ceremonies surrounding the inauguration, to allow for a full state funeral, and many of the military men who participated in the inauguration took part in the funeral. It also meant Johnson's casket traveled the entire length of the Capitol, entering through the Senate wing when taken into the rotunda to lie in state and exiting through the House wing steps due to inauguration construction on the East Front steps.

On March 23, 2007, President George W. Bush signed legislation naming the United States Department of Education headquarters after President Johnson.

Passing the civil rights bill in the House required getting it through the Rules Committee, which had been holding it up in an attempt to kill it. Johnson decided on a campaign to use a discharge petition to force it onto the House floor. Facing a growing threat that they would be bypassed, the House rules committee approved the bill and moved it to the floor of the full House, which passed it shortly thereafter by a vote of 290–110. In the Senate, since the tax bill had passed three days earlier, the anti-civil-rights senators were left with the filibuster as their only remaining tool. Overcoming the filibuster required the support of over twenty Republicans, who were growing less supportive due to the fact that their party was about to nominate for President a candidate who opposed the bill. According to Caro, it was ultimately Johnson's ability to convince Republican leader Everett Dirksen to support the bill that amassed the necessary Republican votes to overcome the filibuster in March 1964; after 75 hours of debate, the bill passed the Senate by a vote of 71–29. Johnson signed the fortified Civil Rights Act of 1964 into law on July 2. Legend has it that the evening after signing the bill, Johnson told an aide, "I think we just delivered the South to the Republican party for a long time to come", anticipating a coming backlash from Southern whites against Johnson's Democratic Party.

With the war still arguably in a stalemate and in light of the widespread disapproval of the conflict, Johnson convened a group called the "Wise Men" for a fresh, in-depth look at the war—Dean Acheson, Gen. Omar Bradley, George Ball, Mac Bundy, Arthur Dean, Douglas Dillon, Abe Fortas, Averell Harriman, Henry Cabot Lodge, Robert Murphy and Max Taylor. At that time McNamara, reversing his position on the war, recommended that a cap of 525,000 be placed on the number of forces deployed and that the bombing be halted, since he could see no success. Johnson was quite agitated by this recommendation and McNamara's resignation soon followed. With the exception of George Ball, the "Wise Men" all agreed the administration should "press forward". Johnson was confident that Hanoi would await the 1968 US election results before deciding to negotiate.