In 1937, Johnson won election to a vacant congressional seat, and he was consistently reelected through 1946. Despite Roosevelt's support, however, he was defeated in a special election to the Senate in 1941. He served (1941-42) in the navy.

In 1948, Johnson was elected U.S. Senator from Texas after winning the Democratic primary by a mere 87 votes. A strong advocate of military preparedness, he persuaded the Armed Services Committee to set up (1950) the Preparedness Investigating Subcommittee, of which he became chairman. Rising rapidly in the Senate hierarchy, Johnson became (1951) Democratic whip and then (1953) floor leader. As majority leader after the 1954 elections he wielded great power, exhibiting unusual skill in marshaling support for President Eisenhower's programs. He suffered a serious heart attack in 1955 but recovered to continue his senatorial command.

Johnson lost the 1960 Democratic presidential nomination to John F. Kennedy, but accepted Kennedy's offer of the vice presidential position. Elected with Kennedy, he energetically supported the President's programs, serving as an American emissary to nations throughout the world and as chairman of the National Aeronautics and Space Council and of the President's Committee on Equal Employment Opportunities. After Kennedy's assassination on Nov. 22, 1963, Johnson was sworn in as president and announced that he would strive to carry through Kennedy's programs.

Congress responded to Johnson's skillful prodding by enacting an $11 billion tax cut (Jan., 1964) and a sweeping Civil Rights Act (July, 1964). In May, 1964, Johnson called for a nationwide war against poverty and outlined a vast program of economic and social welfare legislation designed to create what he termed the Great Society. Elected (Nov., 1964) for a full term in a landslide over Senator Barry Goldwater, he pushed hard for his domestic program. The 89th Congress (1965-66) produced more major legislative action than any since the New Deal. A bill providing free medical care (Medicare) to the aged under Social Security was enacted, as was Medicaid; federal aid to education at all levels was greatly expanded; the Voting Rights Act of 1965 provided new safeguards for African-American voters; more money went to antipoverty programs; and the departments of Transportation and of Housing and Urban Development were added to the Cabinet.

Johnson's domestic achievements were soon obscured by foreign affairs, however. The Aug., 1964, incident leading Congress to pass the Tonkin Gulf resolution gave Johnson the authority to take any action necessary to protect American troops in Vietnam. Convinced that South Vietnam was about to fall to Communist forces, Johnson began (Feb., 1965) the bombing of North Vietnam. Within three years he increased American forces in South Vietnam from 20,000 to over 500,000 (see Vietnam War). Johnson's actions eventually aroused widespread opposition in Congress and among the public, and a vigorous antiwar movement developed.

As the cost of the war shot up, Congress scuttled many of Johnson's domestic programs. Riots in the African-American ghettos of large U.S. cities (1967) also dimmed the president's luster. By 1968 he was under sharp attack from all sides. After Senators Eugene McCarthy and Robert Kennedy began campaigns for the Democratic presidential nomination, Johnson announced (Mar., 1968) that he would not run for reelection. At the same time he called a partial halt to the bombing of North Vietnam; two months later peace talks began in Paris. When Johnson retired from office (Jan., 1969), he left the nation bitterly divided by the war. He retired to Texas, where he died.