The Canadian native was the daughter of actor John Vernon, best known for his portrayal of Dean Wormer in Animal House (1978), and Nancy West, a former actress/model. Her father moved the family to Hollywood, California when Kate was 7 years old. There the future actress originally planned to become an architect, but shortly after high school, her creative aspirations got the better of her, and despite her father's warnings, she elected to try her hand at acting.

In the early- to mid-1980s, she began to land parts in both films and television, including her big-screen debut in her father's film, Chained Heat (1983), followed by the movie Alphabet City, which also starred her then-boyfriend Vincent Spano. Then came Roadhouse 66, starring Judge Reinhold. Both were released in 1984.

After a 1984 guest spot on an episode of NBC's Family Ties (1982-89) entitled "Birthday Boy," there followed a small part in the made-for-TV movie, Flight 90: Disaster on the Potomac. Around that time she also appeared on an episode of Remington Steele before winning her first regular role, as Lorraine Prescott on Falcon Crest, in the 1984-85 season. Soon after that first big brush with notoriety, many other TV and film roles followed, including Pretty in Pink (1986), where she played Benny, the snobby blonde nemesis of Molly Ringwald. After putting in quality John Hughes time, Vernon continued to work steadily, making guest appearances on many TV series and movies.

On the big screen, she landed a small part in the 1992 Spike Lee classic, Malcolm X, where she locked lips with Denzel Washington, before returning to television with the recurring role of Assistant District Attorney Belinda Fox on the NBC drama, L.A. Law. She lasted through the show's final 1994 season. Other recurring roles included the Don Johnson vehicle, Nash Bridges (CBS), where she played the role of Whitney Thomas, and the short-lived 2005 series, Reunion.

Also in 2005, she won the Battlestar Galactica role of Ellen Tigh, the alcoholic wife of second-in-command Colonel Tigh, played by fellow Canadian actor Michael Hogan. Kate's latest projects include the lead role in the Lifetime TV movie Last Chance Cafe and a small role in the DVD movie Safe Harbour.