Roundtree was a virtual unknown, having appeared only in "What Do You Say to a Naked Lady?" (1970), when he was chosen by Gordon Parks to play "Shaft". Based on his success, he landed a variety of roles that included the manager of a daredevil motorcycle rider in "Earthquake" (1974). In 1975, he co-starred with Peter O'Toole in the title role of "Man Friday", a retelling of the "Robinson Crusoe" story in which Friday is not "civilized," and Crusoe commits suicide. After appearing in the disastrous "Inchon" (1982), film roles in the 80s became sporadic and Roundtree found himself generally playing law enforcement types, like the police commissioner in "Maniac Cop" (1988) and the police captain in both "Party Line" (1988) and "A Time to Die" (1991). After a supporting role in David Fincher's "Seven" and a turn as an iceman who sparks a racial incident in Tim Reid's "Once Upon a Time...When We Were Colored" (both 1995), he joined Bernie Casey, Fred Williamson, Pam Grier and other stars of 70s black action films in "Original Gangstas" (1996), in which the older stars--now somewhat paunchy--return for one last go-round. It put some spark into Roundtree's feature film career, as in 1997, he co-starred in both "Steel" (as the junkyard-owning mentor to the title character) and "George of the Jungle" (as the jungle leader Kwame).
On TV, Roundtree had one of his best opportunities in the breakthrough miniseries "Roots" (ABC, 1977), playing a handsome, well-groomed carriage driver with whom Kizzy (Leslie Uggams) falls in love until she sees that when the master (George Hamilton) calls, Roundtree grovels. Roundtree also starred in the miniseries "AD" (NBC, 1985), before having another shot at a series with a supporting role in "Outlaws" (CBS, 1986-1987) as Ice McAdams. By 1990, Roundtree was out of primetime and in the cast of the short-lived multi-racial NBC daytime drama "Generations", playing a doctor forced to live in hiding for 15 years for a murder he did not commit. He co-starred in two "Bonanza" revival movies, "The Return" (NBC, 1993), and "Under Attack" (NBC, 1995), and, during the 1995-1996 season, hosted the UPN specials "Cop Files". Roundtree tried his hand at sitcoms in 1996, playing Dave Chappelle's father in the short-lived "Buddies" (ABC). In 2001, Roundtree was cast in the comedy-crime feature "Corky Romano" and one year later, he toured with the play "Men Cry In The Dark."