Ashby was born in Atlantic Beach, Florida and graduated from The Bolles School, a private school located in Jacksonville, Florida.
He attended Fort Lewis College in Durango, Colorado, but dropped out his junior year to pursue an acting career.
He studied at the Neighborhood Playhouse in New York alongside Tom Cruise and Dylan McDermott.
His first big role came in 1987 when he played Lawrence Graf von Haugwitz-Hardenberg-Reventlow in a TV movie about the real life playboy and his mother, socialite Barbara Hutton. The film, Poor Little Rich Girl, went on to win the Golden Globe for best miniseries that year.
His most recognized role is his role of Johnny Cage in the martial arts film, Mortal Combat in 1995.
He is well known for his work on the nighttime soap Melrose Place. Ashby played Dr. Coop Cooper for two seasons in 1997 and 1998.
Ashby did a number of notable guest roles on popular shows in the late 80s and 90s including China Beach and MacGyver. He met his wife, actor Susan Walters, while filming a guest role on the ABC daytime drama LOVING in 1989. Walters also appears on MTV's Teen Wolf as Lydia's mother. Ashby returned to soaps in 2003 taking on the role of Cameron Kirsten on The Young and the Restless. Most recently, in 2008, he played Paul Hollingsworth on Days of Our Lives.
In 2007, he appeared as Chase in in the feature film Resident Evil: Extinction.
Teen Wolf is not Ashby’s first brush with lycanthropy, he fell victim to the titular character in Fox Television’s short-lived series Werewolf back in 1987.