He was elected as a Democrat to the Alabama House of Representatives in 1974 and served from 1975 until 1981 and in the Alabama Senate from 1981 until 1992. Hilliard was elected to the United States House of Representatives in 1992. He faced his first serious re-election challenge from Artur Davis in the 2000 Democratic primary election but prevailed.
Davis challenged Hilliard 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 that year was focused on race and the Middle East. Hilliard"s surrogates claimed that all Davis, also an African American, had done for African Americans as a federal prosecutor was to "put them in jail".
In 2001 Hilliard voted against a bill funding increases in military support to Israel and opposing criminalization of Palestinian politicians. Hilliard is a 1960 graduate of Western-Olin High School in Birmingham, Alabama.
He received a Bachelor of Arts in 1960 from Morehouse College, a Juris Doctor in 1967 from Howard University, and an Master of Business Administration in 1970 from Atlanta University.
He is a member of Alpha Phi Alpha fraternity. He is a member of the board of the Congressional Black Caucus Institute. Hilliard"s son, Earl Hilliard, Junior., is a former member of the Alabama House of Representatives who ran unsuccessfully for Congress in 2010, also in the 7th district.