Roundtree was a leading man in early 1970s blaxploitation films, his best-known role being Detective John Shaft in the hugely popular action movie Shaft. He also played the slave Sam Bennett in the 1977 television series Roots. He portrayed Dr. Daniel Reubens on Generations from 1989-1991. Prior to becoming an actor, he was a football player and a model. Although Roundtree worked through the 1990s, many of his more recent films were not well-received, but he was able to find success in stage plays.
Since 1990, however, he reemerged as a cult icon. Roundtree appeared in David Fincher's critically acclaimed 1995 movie Seven, the 2000 remake of Shaft as John Shaft's uncle, and guest-starred in several episodes of the first season of Desperate Housewives as an amoral private detective. He also appeared in 1997's George of the Jungle, as well as playing a high school vice-principal in the 2005 movie Brick. His voice was also utilized as the title character in the hit Play Station game Akuji the Heartless, where Akuji must battle his way out of the depths of hell at the bidding of the Baron.
In 1997, Roundtree had a leading role in the short-lived FOX ensemble drama 413 Hope St. He portrayed Booker T. Washington in the 1999 television movie Having Our Say: The Delany Sisters' First 100 Years.
He has appeared in the television series The Closer as Colonel D.B. Walter U.S.M.C. (retired) father of sniper and in Heroes as Simone's terminally ill father, Charles Deveaux. Next, he appeared in an episode of Lincoln Heights. Most recently, Roundtree has a supporting role in the 2008 Speed Racer film as a racer-turned-commentator who is an icon and hero to Speed.
He also appeared in the two-parter in Season 1 of the Second Generation of Knight Rider as the father of FBI Agent Carrie Ravai