In 1989, he was principal defense counsel for U.S. District Judge Walter L. Nixon, Jr. of Biloxi, Mississippi, in an impeachment trial before the United States Senate.

For ten years, Stewart wrote the monthly "Supreme Court Report" for the American Bar Association Journal.

In February 2015, Simon & Schuster released Stewart's next nonfiction book, Madison's Gift: Five Partnerships that Built America.

In September 2013, Kensington Books published his first novel, The Lincoln Deception, which explores the secrets of the John Wilkes Booth conspiracy.

Impeached, for example, counters the view, once best known from Profiles in Courage by John F. Kennedy and Theodore Sorensen, that the acquittal of Andrew Johnson was a triumph of bravery over politicking.

Stewart has countered this view with evidence, some of which had come out in hearings under Representative Benjamin Butler soon after the acquittal, that senators had been led to vote to acquit by offers of patronage and money.