Born 11 October 1888 in St. George, Utah, Walter Keil Granger moved with his parents to Cedar City in 1894, where he attended the public schools. He graduated from a branch of the University of Utah at Cedar City in 1909 and later attended the Branch Agricultural College at Cedar City. He engaged in agricultural pursuits and livestock raising and was a well-known farmer in the Cedar City area.

For a time Granger was a member of the board of trustees of Utah State Agricultural College, and he served as Cedar City postmaster from 1914 to 1922, including the time he was in France as a Marine sergeant during World War I. Well liked by the people of Cedar City, he was elected mayor from 1923 through 1926 and again from 1930 through 1932. Granger was a member of the Utah House of Representatives from 1932 to 1937 and was Speaker of the House in 1935. From 1937 to 1940 he was a member of the Utah Public Service Commission.

Elected as a Democrat to the United States Congress for six terms, Granger served as a congressman from 1940 to 1952. In 1954 he was an unsuccessful candidate for election to the United States Senate. He returned to his farming interests, but continued public service as a member of the Board of Appeals of the United States Forest Service from 1967 to 1970. In 1976 he was awarded an honorary degree from Southern Utah State College.

Granger was an active member of the LDS Church, having served for nine years as bishop of the Cedar Third Ward. He died in Cedar City on 21 April 1978 and was survived by his widow, Hazel Dalley, whom he had married in 1912. He was buried with full military honors in the Cedar City Cemetery.