Hilliard was born in Birmingham, Alabama and he graduated from Morehouse College. Hilliard was elected to the Alabama house of representatives as a Democrat in 1974. He served in the Alabama house from 1975 to 1981 and the Alabama Senate from 1981 to 1992. Hilliard was elected to the House of Representatives in 1992 after the state legislature created Alabama's first black-majority Congressional district, connecting black areas in Birmingham, Montgomery, Selma, and the Black Belt, as a condition of the Voting Rights Act. In 1997, Hilliard traveled to Libya despite U.S. sanctions against Libya at the time.

Hilliard faced his first serious re-election challenge from Artur Davis in the 2000 primary election, but prevailed. He faced Davis again in 2002 in a district that had been changed significantly by redistricting, adding many white voters in Birmingham and losing its mostly black portion of Montgomery. The campaign in 2002 was focused on race and the Middle East. Hilliard's surrogates claimed that all Davis did for African Americans as a federal prosecutor was "put them in jail". In 2001 Hilliard voted against a resolution supporting Israel's fight against terrorism, and consequently Davis received donations from pro-Israeli groups. Hilliard won the first primary, but he didn't win a majority, so he faced Davis in a run-off election. Davis won the run-off with 54f the vote.

Hilliard is a member of Alpha Phi Alpha, the first intercollegiate Greek-letter fraternity established for African Americans.