He rose to prominence for his role as Theodore Huxtable on the NBC sitcom The Cosby Show (1984–1992), which earned him a nomination for Outstanding Supporting Actor in a Comedy Series at the 38th Primetime Emmy Awards.

In 2015, he received a Grammy Award for Best Traditional R&B Performance for the song "Jesus Children" alongside Robert Glasper Experiment and Lalah Hathaway.

During his tenure on The Cosby Show, Warner turned his hand to directing, making music videos including New Edition's "N.E.

Heart Break" (1989), rapper Special Ed's "I'm the Magnificent" (1989),[3] and British R&B group Five Star's "I Love You For Sentimental Reasons" (1994).

In 2011 and 2012, he guest starred in four episodes of the NBC series Community as Andre, the ex-husband of Shirley Bennett (Yvette Nicole Brown).

In 2012, Warner was nominated for Outstanding Actor in a comedy series at the NAACP Image awards for his role in Reed Between the Lines.

He also played the role of parole officer James Bagwell on Amazon Prime's show Sneaky Pete and as Dr. AJ "The Raptor" Austin on FOX's The Resident.

Warner had a relationship with actress Michelle Thomas, who portrayed his girlfriend Justine Phillips on The Cosby Show, until 1994 and was at her bedside when she died in 1998.