In 1933, King became a member of the California State Assembly and served in that body until 1942, with the exception of 1936. From July 15, 1940 to July 18, 1940, King served as a delegate from California to the 1940 Democratic National Convention at Chicago Stadium in Chicago, Illinois. The representative for California's 17th congressional district, Lee E. Geyer, died in Washington, D.C. on October 11, 1941. King served out Geyer's unfinished term, and was elected as a Democrat to the 77th United States Congress by a special election on August 25, 1942. Later that year, King ran unopposed in the November 3 election and captured 92,260 votes, 99.8 percent of the total. King served as a member of the United States House Committee on Ways and Means, beginning a commitment that he would serve during twelve of his following thirteen terms in the House of Representatives, excluding only 1947-1948, during the 80th United States Congress. Two years later, King again served as one of California's delegates to the 1944 Democratic National Convention again held at Chicago Stadium from July 19 to July 21. In the House elections on November 7, 1944, King again ran unopposed for state's 17th district, and captured 147,217 votes, nearly 100 percent. In the 1946 House elections, King was again unopposed and captured 110,654 votes, or 99.4 percent. At the 1948 Democratic National Convention, King served as an alternate delegate from California. In continuance of the trend, he again ran unopposed in 1948 and 1950 and captured 99.9 percent of the vote in both elections. During the 1950s, King also served as the chairman of the House of Representatives subcommittee investigating tax irregularities. After facing his first competitive re-election bid in 1952 when he defeated Republican challenger Robert Finch by nearly 11 percent of the vote, King cruised by in future elections, capturing more than 60 percent of the vote in landslide elections in each biennial election from 1954 to 1966. King also was one of the first people involved in the issue of Medicare, and had carried on the battle in the House of Representatives throughout the 1950s and 1960s until President Lyndon B. Johnson signed the Medicare Bill on July 30, 1965. After nearly twenty-seven years of service, King was not a candidate for re-election in the 1968 House elections to the 90th United States Congress. His successor, Glenn M. Anderson, won a close election by a slim two percent margin. On March 17, 1974, King died of a stroke at a nursing home in Inglewood, California at the age of 76. He was then interred in Inglewood Park Cemetery in Inglewood, California.
