Warner was born in Jersey City, New Jersey. He was raised by his divorced mother, Pamela, who served as his manager. He was named after Malcolm X and jazz pianist Ahmad Jamal. At the age of nine, he demonstrated an interest in show business which led to enrollment in acting schools. His active career as a child later led him to graduate high school from The Professional Children's School in New York City, New York.
With appearances and roles on many television shows and films, he landed his most successful role as Theo Huxtable, the only son of Heathcliff Huxtable, who was played by Bill Cosby on the NBC sitcom, The Cosby Show from 1984 to 1992. Warner auditioned for the role on the very last day of the nationwide search and was chosen by Cosby himself.
He also starred in Jeremiah, was the voice of The Producer character on The Magic School Bus and co-starred with comedian Eddie Griffin for four years on the UPN sitcom Malcolm & Eddie. Warner continued his career on the CBS sitcom Listen Up! with Jason Alexander and the host of the literacy-promoting children's show CBS Storybreak. He guest-starred on an episode of The Fresh Prince of Bel Air playing the role of Hilary's boyfriend, and has directed several music videos including British R&B group Five Star's "I Love You For Sentimental Reasons" (1994) as well as many sitcom episodes including The Cosby Show, All that, Kenan & Kel, and Malcolm & Eddie. Also In 1988 Warner was In New Edition's 1988 Music Video N.E Heartbreak.
In addition, Warner directed the acclaimed, teen-oriented public health video Time Out: The Truth About HIV, AIDS, and You (1992), which featured Arsenio Hall and Earvin "Magic" Johnson discussing the realities of HIV and AIDS and the best ways to prevent its spread.
In 2003, Warner released his debut EP, The Miles Long Mixtape. In 2007, Warner followed up with his second CD entitled Love & Other Social Issues. In 2009 he guest starred in an episode in the new TNT series HawthoRNe. In 2011 he guest starred in an episode of the NBC series Community as the ex-husband of Shirley Bennett (Yvette Nicole Brown). His character subtly referenced his Cosby Show past by wearing a "Cosby sweater" that he stated was from his dad.
He is a bass guitar player and a performance poet, and has performed at the National Black Theatre Festival since 2003, in addition to hosting its Poetry Jam.
Warner's co-starred in BET's scripted comedic television series Reed Between the Lines. He played the role of Alex Reed, an English professor married to Carla Reed, a psychologist played by former Girlfriends star Tracee Ellis Ross. The couple had three children: Kaci and Kenan Reynolds, Carla's children from a previous relationship, and Alexis Reed, their child together. The show highlighted the couple's ups and downs together as a blended family. 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.
In the spring of 2015, it was announced that Warner would be playing the part of Al Cowlings in the crime series American Crime Story, based on the events of the O.J. Simpson trial.
Warner portrays recurring characters on multiple current TV series. He played prison counselor Julius Rowe on the sixth season of USA network's Suits. On the TNT series Major Crimes he portrays Lt. Chuck Cooper, a member of the LAPD's Special Investigation's Section (SIS) and the love interest of the Major Crime Division's Detective Amy Sykes. He also plays the role of parole officer James Bagwell on Amazon Prime's show Sneaky Pete.
Warner had a relationship with actress Michelle Thomas, who portrayed his girlfriend on The Cosby Show, and was at her bedside when she died in 1998. He was in a relationship with actress Karen Malina White for seven and a half years.The Miles Long Mixtape (2003)
Love & Other Social Issues (2007)
Grammy Awards2015: Won, "Best Traditional R&B Performance" - "Jesus Children" (with Robert Glasper Experiment featuring Lalah Hathaway)
MD Theatre Guide Readers' Choice Awards2013: Winner 1st Place, "Best Performance by Lead Actor in a Play" -Doctor John Prentice in Guess Who’s Coming to Dinner at Arena Stage
BET Comedy Awards2005: Nominated, "Outstanding Supporting Actor in a Comedy Series" — Listen Up
Emmy Awards1986: Nominated, "Outstanding Supporting Actor in a Comedy Series" — The Cosby Show
Image Awards1996: Nominated, "Outstanding Supporting Actor in a Drama Series" — Touched by an Angel
2001: Nominated, "Outstanding Actor in a Comedy Series" — Malcolm & Eddie
2012: Won, "Outstanding Actor in a Comedy Series" - Reed Between the Lines
TV Land Awards2006: Nominated, "Favorite Singing Siblings" — The Cosby Show (shared w/co-stars)
Young Artist Award1985: Won, Best Young Supporting Actor in a Television Comedy Series - The Cosby Show
1988: Nominated, Best Young Male Superstar in Television - The Cosby Show
1989: Won, Best Young Actor/Actress Ensemble in a Television Comedy, Drama Series or Special - The Cosby Show (shared w/co-stars)
1990: Won, "Best Young Actor Supporting Role in a Television Series" — The Cosby Show
Theo and Me: Growing up Okay (1988) - ISBN 0-525-24694-0 (with Daniel Paisner)