First coming to attention as a child actor in the original 1959 Broadway production of A Raisin in the Sun, Turman is known for his roles as Lew Miles on the prime-time soap opera Peyton Place (1968–1969), high school student Leroy "Preach" Jackson in the 1975 coming-of-age film Cooley High, math professor and retired Army colonel Bradford Taylor on the NBC sitcom A Different World (1988–1993), and Baltimore mayor Clarence Royce on the HBO drama series The Wire.

[3] Turman had his first prominent acting role at the age of 12 as Travis Younger in the original Broadway production of Lorraine Hansberry's classic play, A Raisin in the Sun, opposite Sidney Poitier, Ruby Dee, Claudia McNeil, Ivan Dixon, Louis Gossett Jr., Lonne Elder III, John Fiedler and Diana Sands.

[citation needed] On television, he has directed episodes of The Parent 'Hood, Hangin' with Mr. Cooper, A Different World, and The Wayans Bros. Turman began his film career in the 1970s with blaxploitation flicks including Five on the Black Hand Side (1973), Thomasine & Bushrod (1974) and Together Brothers (1974), then progressed to roles in Cooley High (1975), plus The River Niger (1976), J. D.'s Revenge (1976) and A Hero Ain't Nothin' but a Sandwich (1978).

More notable films include Penitentiary II (1982), Gremlins (1984), Deep Cover (1992), How Stella Got Her Groove Back (1998), Men of Honor (2000), Sahara (2005), Kings of the Evening (2007), Burlesque (2010) and Super 8 (2011).

Turman's other television appearances include Hawaii Five-O (as Harley Dartson, 1973, "Tricks Are Not Treats"), the Twilight Zone segment "Paladin of the Lost Hour" (co-starring Danny Kaye with a script by Harlan Ellison), Matlock, Millennium, and the sitcom All of Us.

His character is the imprisoned father of Nate Lahey (Billy Brown), a former police officer, detective and lover to series star Annalise Keating (Viola Davis).

Turman founded Camp Gid D Up to teach horse skills and values to urban youth in southern California and has been co-grand marshal for the Bill Pickett Invitational Rodeo, celebrating black cowboys, for nearly 40 years.