Stewart attended modeling school before being hired by Tommy Hilfiger Company. She has also designed shoes independently. Stewart, along with model Meagan Maitland, is the current face of Australian underwear line, Antz Pantz. Stewart is currently signed with Nous Models.

She also has her own clothing line called Pinky Star Fish.

Stewart has been a co-host on The Insider.

During 2005, there were rumors that she would replace Nicole Richie and join Paris Hilton in the fourth season of reality show The Simple Life; however, FOX later announced that the show was to be cancelled. E! picked up the fourth season in which Richie returned.

Stewart has since shot the pilot for her own MTV reality series; Win Your Life Back. It is not yet known if MTV have picked up the series. She has also appeared on MTV's Cribs and was a regular on Celebrities Uncensored

Stewart's acting debut was a guest role on the series Undeclared.

Stewart is also said to be following her father's footsteps and pursuing a music career. Stewart, who plays violin and piano was approached by a producer in 2005, and after doing some test-runs in a studio, has since been taking singing lessons. Stewart believes music is in her blood, and hopes to have an album complete by mid-2007.

As well as coming from a rich and well known family, Kimberly Stewart is well-known in US tabloids for her many celebrity-friendships, including Paris and Nicky Hilton, Nicole Richie, Courtney Love, Anna Nicole Smith, Caroline D'Amore and Bobby Trendy.