Initially an isolationist on foreign policy, he took a more internationalist stance in later years; he retired after a narrow defeat for a fourth term in 1962.

Capehart's career in the music industry made him wealthy and provided a path to the national political stage.

[5][6] Capehart was first elected to the U.S. Senate in 1944, narrowly defeating Henry Schricker, going on to win subsequent victories in 1950 against Alexander M. Campbell and in 1956 against Claude R. Wickard.

When first elected to the Senate at the height of World War II, Capehart supported efforts to compromise with the Japanese on terms of surrender in the summer of 1945 when minority leader Wallace H. White, Jr. stated that the war might end sooner if President Truman would state specifically in the upper chamber just what unconditional surrender meant for the Japanese.

[7] Throughout the 1950s, Capehart was constantly at odds with his Senate colleague William E. Jenner, a staunch isolationist Republican who consistently opposed President Eisenhower's "modern-Republicanism."

Capehart, believing the bill was socialistic in nature, and lacking enough support to kill it, introduced an amendment which would have reduced the authorization to 35,000 units.

[12] Capehart was also an advocate of clean air legislation, and briefly served on the United States Senate Select Committee on Improper Activities in Labor and Management with Kennedy, Barry Goldwater, and Karl Mundt.

He retired to his farming and business interests in Indiana, occasionally returning to Washington to provide both foreign policy and domestic-issue advice; jaded by the Watergate scandal, he became increasingly critical of President Richard Nixon.