King was born in St. Louis, Missouri, and was the youngest of seven children in her family. She graduated from University of Missouri and later moved to New York to pursue an acting career, appearing on stage productions. In mid-1990s, King moved to Los Angeles, California, when she began appearing on television shows such as The Wayans Bros., Living Single, Malcolm & Eddie, Murphy Brown, and Any Day Now.
King has appeared in a number of films, playing small parts, include Magnolia (1999), Dude, Where's My Car? (2000), Bubble Boy (2001), The Life of David Gale (2003), Dogville (2003), Dreamgirls (2006), Pineapple Express(2008), The Hangover (2009), and Valentine's Day. She guest-starred on more than 50 shows, include NYPD Blue, Ally McBeal, Six Feet Under, The West Wing, CSI: Crime Scene Investigation, NCIS, and Ugly Betty.
From 2001 to 2002, King had the recurring role as Helene Parks in the Fox drama series, Boston Public created by David E. Kelley. In 2003, she co-starred in the short-lived CBS drama The Brotherhood of Poland, New Hampshire, also created by Kelley. In 2006, she played Aunt Lou in the HBO drama series Deadwood during its third and final season. In 2009, King had the recurring role as Neeta, the nanny of Jax Teller's son in the FX drama series, Sons of Anarchy.
In 2010, King was cast in the series regular role as grandmother, Rosetta McMillan "Nana", in the CBS sitcom Mike & Molly, even though she is only 7 years older than Reno Wilson (who plays her grandson, Carl).
She also appears regularly in Netflix's adaptation of A Series of Unfortunate Events (TV series), 2017.