Willis held the congressional seat for ten terms. He was the chairman of the Committee on Un-American Activities during the 88th, 89th, and 90th congresses (1963–1969). He supported anti-communist Cold War laws, such as the McCarran-Walter Internal Security Act of 1950. Willis was in effect the last chairman of the HUAC, which was reconstituted as the Committee on Internal Security in 1969. During the 1960s, Willis viewed both the civil rights movement and opposition to the Vietnam War as reflections of communist influences. Having been a signatory to the 1956 Southern Manifesto that opposed the desegregation of public schools ordered by the Supreme Court in "Brown v. Board of Education", he voted against the Civil Rights Act of 1964 and the Voting Rights Act of 1965. He also spoke out against the radicalism of the Ku Klux Klan.