While she continued modeling for a time after her marriage, Castelbajac shifted over time to the business side as well as doing journalism. She began her business career in 1983, working as the accessory director for her husband's design company, Jean Charles de Castelbajac, SA., a position she continued until her divorce in 1995. She also began to contribute articles to "InStyle" magazine in 1989, and accepted a position as a founding editor of the women's magazine "Mirabella", covering European trends. "Harper's Bazaar" said of her, "Accomplished, charming and refreshingly candid, Kate brings her personal brand of elan to everything she does."