Keller was elected as a Democrat to the Seventy-second and to the four succeeding Congresses (March 4, 1931-January 3, 1941). He was an unsuccessful candidate for reelection in 1940 to the Seventy-seventh Congress and for election in 1942 to the Seventy-eighth Congress and in 1944 to the Seventy-ninth Congress. He engaged in literary work and lecturing. He served as special adviser to the United States Ambassador at Mexico City from June 1945 to August 1946. He was an unsuccessful candidate for election in 1948 to the Eighty-first Congress and in 1950 to the Eighty-second Congress. He died in Ava, Illinois, September 3, 1954. He was interred in Ava Evergreen Cemetery.