After graduating from Bolles High School in Jacksonville, Florida, Ashby took a degree in psychology and business administration at Fort Lewis College in Durango in the state of Colorado, and then moved to New York where he took drama classes in the Neighborhood Playhouse. Early in his career he took part in the soap opera Loving, and an episode of MacGyver, also got a small role in the 1990 movie Mr. & Mrs. Bridge with Paul Newman and again in 1990 he starred in the independent film The queen of hell alongside Karen Black. Then in 1991 he starred opposite Kelly Preston in the movie thriller The Perfect Bride. In 1992 he took part in three independent films including the film Shot Gun with Michael Pare. In 1994 he appears in 8 seconds of glory, with Luke Perry and Wyatt Earp opposite Kevin Costner. However, the role that made him famous is that of Johnny Cage in Mortal Kombat martial arts film, based on the popular video game starring opposite Christopher Lambert. To prepare for this role, the actor trained for two months practicing martial arts. In 1996 he starred opposite Eric Roberts in the movie thriller Dark Angel. Then in 1997 he starred in the action film entitled Blast directed by Albert Pyun starring opposite Rutger Hauer, playing Jack Bryant and a former champion of Tae Kwon Do who is forced to use all his martial arts skills to fight the crazy plan of ruthless terrorists who want to blow the Olympic swimming pool in Atlanta where the Olympic Games are underway (a clear reference to the Olympic Games of 1996 in Atlanta where there was really an attack). In 1998 he starred in The Mystery of the Lake and then took part in 35 episodes of the show Melrose Place where he plays the role of the handsome doctor Bret Cooper. In 2002 he participated in the action movie Sniper 2 - Suicide Mission, opposite Tom Berenger and an episode of the TV show CSI: Crime Scene Investigation. In 2004 he starred in Wild Things 2 and meanwhile took part in 55 episodes of the soap opera Young and the Restless, where he played the cynical murderer Cameron Kirsten. In 2005 resumed the role of Detective Morrison in the film Wild Things 3. In 2006 he starred in Bridesmaid and in 2007 took part in the film Resident Evil: Extinction next to Milla Jovovich. Then in 2008 he starred in the horror movie What Prom and the soap opera Days of our lives. In 2008 he starred in Impact Point and starred with Steven Seagal in the action film Last Night - Death in the night. In 2009, he starred in action Anaconda - Trail of Blood. 2011-2012 he played the role of Sheriff Stilinski in the TV series Teen Wolf.