Lumbly made his film debut as an inmate in Don Siegel's "Escape From Alcatraz" (1979). He went on to appear in forgettable fare ("Caveman" 1981) and cult favorites ("The Adventures of Buckaroo Banzai: Across the 8th Dimension" 1984) before earning praise for his performance as a football hero in Taylor Hackford's "Everybody's All-American" (1988). In Charles Burnett's "To Sleep With Anger" (1990), he was the hardworking, successful Junior resentful of his younger brother (Richard Brooks). Later that same year, he was the tenant displaced in favor of psycho Michael Keaton in John Schlesinger's "Pacific Heights". In Steve Anderson's "South Central" (1992), Lumbly was Ali, an older, Muslim convict who acts as mentor to a fellow convict (Glenn Plummer).

On TV, Lumbly played a local clergyman in the biopic of a Gary Rowe Jr who went "Undercover With the KKK" (NBC, 1979) before appearing as Petrie in the TV-movie "Cagney & Lacey" (CBS, 1981) which spawned the series. For six years, he appeared in support of Tyne Daly and the three actresses who played her partner (Loretta Swit in the original, Meg Foster in the first season, and Sharon Gless). He reprised the role in four reunion specials that aired between 1994 and 1996. In 1985, Lumbly recreated his stage role as Theseus in the PBS production of "The Gospel at Colonus" and went on to play Bobby Seale in "Conspiracy: The Trial of the Chicago Eight" (HBO, 1987) and slave uprising leader Denmark Vesey in "Brother Future" (PBS, 1991). Other series work included a recurring role as a professor accused of murder on "L.A. Law" (NBC, 1989-90), the chief administrator of a Caribbean medical school in "Going to Extremes" (ABC, 1992-93) and the paraplegic man who becomes a superhero through technology in "M.A.N.T.I.S." (Fox, 1994). The latter series was low-rated, but pleas from groups wanting positive Black adult roles in a drama convinced the Fox network to keep it on. Eventually, it became a ratings victim. Lumbly also appeared opposite Diana Ross in her TV-movie debut, "Out of Darkness" (ABC, 1994). He was one of a number of leading African American stars in "America's Dream" (HBO, 1996), a collection of three short pieces about African American life. Lumbly is married to actress Vonetta McGee who appeared as his wife on "Cagney and Lacey" and in "To Sleep With Anger".