In 1946, Brooks began his career in public service when he was elected to represent Jefferson County in the Texas Legislature. Brooks was elected to the U.S. Congress in 1952, where he served for the next five decades until 1995. 

As a member of the influential Texas congressional delegation, Brooks became a close friend of powerful House Speaker Sam Rayburn and Senate Majority Leader Lyndon B. Johnson during the 1950s. 

As a ranking member of the Judiciary Committee, Brooks helped write the Civil Rights Act of 1964 and the Voting Rights Act of 1965; he was one of the few southern congressmen to support civil rights legislation.