He has also had roles in various superhero franchises including voicing Martian Manhunter in the DC Animated Universe (DCAU) and playing M'yrnn J'onzz on The CW's Supergirl (2017–2019) set in the Arrowverse.

He stayed with the improvisational company for two years and later moved to San Francisco where he discovered a newspaper ad seeking “two black actors for South African political plays.” He went to the audition and landed one of the parts (along with then-unknown Danny Glover).

In 1985, he appeared as Theseus in The Gospel At Colonus, an African-American musical iteration of the Oedipus legend on PBS's Great Performances series.

In 1987, he garnered positive reviews for his portrayal of Black Panther Party co-founder Bobby Seale in the HBO television film Conspiracy: The Trial of the Chicago 8.

[6] From 1989 to 1990, he portrayed ongoing character Earl Williams (named for the prisoner in Ben Hecht and Charles MacArthur's story The Front Page), a teacher falsely accused of the rape/murder of a female student, in the series L.A.

Also in 2000, Lumbly guest starred in the season one The West Wing episode "Six Meetings Before Lunch" as Jeff Breckenridge, a nominee for U.S. Assistant Attorney General who supports reparations for slavery.

In 2021, Lumbly guest starred in several episodes of the Disney+ series The Falcon and the Winter Soldier (2021) as Isaiah Bradley, set in the Marvel Cinematic Universe (MCU), and reprised his role in the feature film Captain America: Brave New World (2025).