A daughter of a former model, Stewart always wanted to follow her mother's footsteps. She attended a modeling school before being hired by Tommy Hilfiger Company. Stewart, along with Meagan Maitland and Nicky Hilton, was the face of Australian underwear line, Antz Pantz in 2005-2006.As a part of her duty, she became model for the line's TV commercials and poster adverts. In 2006 she became the face of Blend jeans. She also has her own clothing range called Pinky Star Fish and has designed shoes independently.

In a poll based on wealth and looks run by Britain's FHM magazine in 2007, Kimberly was voted most eligible bachelorette.

In spring 2007, Stewart was seen as the face of two high-profile campaigns; the British Optician chain Specsavers and most notoriously Michelle Mone's Ultimo Lingerie line.

Stewart is currently signed with Nous Model Management in Los Angeles.