Stewart was born in New York City and raised in New York and at her parents' homes in Westport, Connecticut and Easthampton, New York. Her father, Andrew Stewart, and her mother divorced in 1990. Stewart attended prep school at The Putney School in Vermont and graduated from Barnard College, her mother's alma mater.

Stewart has referred to herself as her mother's "original apprentice" and reports that her first job was assisting in Martha Stewart's Westport-based catering business. However, after college, she ventured into other endeavors. She designed, built and operated the Bridgehampton Motel property in Bridgehampton, New York on Long Island. She also bought, built and ran the East Hampton Gym and Sag Harbor Gym on Long Island, which she now co-owns with her partner Bruce Cotter.

Stewart currently co-hosts "Whatever", a show on Martha Stewart Living Radio carried on Sirius Satellite Radio. Stewart and radio partner Jennifer Koppelman Hutt talk about topics ranging from pop culture to personal relationships. The show is billed as being about "whatever" the two women are thinking, reading, or hearing.

--Wikipedia