He is known for playing strict authoritarian characters, including Warden Samuel Norton in the 1994 prison drama The Shawshank Redemption, Chief George Earle in 1993's Demolition Man, Dr. Walcott, the domineering dean of Virginia Medical School in Patch Adams, and Secretary of State Cyrus Vance in Argo.

He also played Leland Owlsley in the Daredevil television series, Secretary of Defense Ethan Kanin in 24, and Noah Taylor in Desperate Housewives.

[3][4] He served in the United States Army (1969–71) as a radio telephone operator with the 2nd Battalion, 501st Infantry Regiment of the 101st Airborne Division, and was at the Battle of Fire Support Base Ripcord, South Vietnam, during the 23-day siege.

[6][7] Gunton played the role of Juan Perón in the original 1980 Broadway production of Evita, earning a nomination for Tony Award for Best Featured Actor in a Musical for his performance.

Additional Broadway credits include Working, King of Hearts, The Music Man (NYCO), How I Got That Story, and Big River.

He signed on as series regular afterward and reprised the role of Kanin but now as the Chief of Staff to the new president, Allison Taylor, in the show's seventh season as well as the two-hour television prequel film, 24: Redemption.