Her first feature film role was in the comedy Hardbodies (1984). Her best-known roles include the horror movie Halloween 4: The Return of Michael Myers (1988) as Kelly Meeker and in Bride of Re-Animator as the title character. She played the title role in CIA Code Name: Alexa, which she reprised in the sequel CIA II: Target Alexa. Her most recent film was Lime Salted Love (2005).

She starred on television series such as Santa Barbara as Marilyn Cassidy in 1992 and her big role was in the 1990s syndicated television series Renegade as Cheyenne Phillips from 1992–1996. She was married to Lorenzo Lamas, who starred as the main character on the series. She was reportedly dropped from the series in 1996 when she made derogatory comments in the press about Lamas Future wife Shauna Sand, who had been making appearances on the show. They later divorced. She is also divorced from actor Jere Burns and Doug Swander. She has made guest appearances on such television series as Dallas, Baywatch, Silk Stalkings, V.I.P. and Days of Our Lives.

Kathleen is currently involved in a variety of projects as a Writer, Director and Director of photography. She also has a flourishing photography Business in the Los Angeles area, and has just released a yoga video called "Kathleen Kinmont's Restorative Core Yoga". In 2012, she contributed several articles on the topic of divorce through The Huffington Post.