Harry Zell Thomason was born in Hampton, Calhoun County, Arkansas, on November 28, 1940.
Thomason played high school football in Hampton under coach Boyd Arnold. After graduating from college, Thomason taught art and drama and coached football at McClellan High School in Little Rock.
Thomason began his film career by producing campaign commercials for Arkansas politicians, including Senator David Pryor. In the early 1970s, he began writing and producing movies, including The Great Lester Boggs and So Sad About Gloria. Thomason's early television credits include The Fall Guy and the miniseries, The Blue and the Gray.
In 1983, he founded Mozark Productions with his wife, Linda Bloodworth-Thomason. They are best known for the television series, Designing Women, which helped to change public perception of Southerners, Evening Shade, named for a small town in Sharp County, Arkansas, and Hearts Afire, starring John Ritter and Billy Bob Thornton.
Thomason has produced and directed several documentaries about Bill and Hillary Clinton: The Man from Hope, Legacy (Bill Clinton Retrospective – 2000 DNC), Hillary 2000 (NY Primary), and The Hunting of the President. Thomason was cochair of the Presidential Inauguration Committee following Clinton's election in 1992.