Stewart was born in Anniston, Alabama and attended the University of Alabama both in undergraduate and in law school. During his years in law school, he ran a successful campaign for SGA president, one of the few to have beaten the Machine.

He was elected as a Democrat to fill the unexpired U.S. Senate term of James B. Allen, who died in office, and whose seat was held in the interim by Maryon Pittman Allen. He served in the Senate from November 8, 1978 to his resignation on January 2, 1981, one day before his term was to end. He lost his bid for reelection in 1980, when he was defeated in the Democratic primary by Jim Folsom, Jr..

One of the key reasons for his defeat in his run for re-election was the support of his opponents by the Texas Bass brothers. The Bass family took great insult from Stewart fairly questioning their undue and likely illegal "cornering" of the silver markets causing a huge runup in silver prices. And in their questioning before the Senate committee investigating this fact by Stewart, the Bass family decided to remove Stewart from office by preventing his re-election.

He presently practices law in Alabama, including as lead attorney on a recent class action lawsuit against agricultural biotech giant Monsanto for PCB dumping in his hometown of Anniston. The case garnered national attention, including coverage by 60 Minutes. As of 2002, the company had paid out as much as $160 million against various plaintiffs in Alabama, including those represented by Stewart.

He also serves on the advisory board of the Blackburn Institute, to which he has reportedly contributed significant funds.