Ashby was born in Atlantic Beach, Florida and graduated from The Bolles School 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 Lance Reventlow in the TV movie Poor Little Rich Girl: The Barbara Hutton Story. The film went on to win the Golden Globe for best miniseries that year. It would also lead him to guest roles in shows like Werewolf, China Beach, MacGyver, Adam-12, The Love Boat: The Next Wave, CSI: Miami and The Gates.
Ashby took part in Kevin Costner’s epic Wyatt Earp in 1994 with future Teen Wolf co-star Ian Bohen. A year later, he would have the starring role of Johnny Cage in Mortal Combat which became his most recognized role. His other film work includes Resident Evil: Extinction, Judgement Day, Wild Things 2, Prom Night, Accused at 17, Anaconda: Trail of Blood, and Iron Man 3.
He is also known for his work on the nighttime soap Melrose Place. Ashby played Dr. Coop Cooper for two seasons in 1997 and 1998. He worked other soap operas such as The Young and the Restless and Days of Our Lives.
Jeff Davis remembered him in Mortal Combat and wanted him to be in his new show. Ashby, who had moved to Atlanta at the time, accepted the role of the Sheriff which he was nominated for a Saturn Award for Best Supporting Actor in 2017 for his work in Season 6.
His character started off as recurring before finally becoming a main character in Season 6. He is also made his directorial debut with the episode Face-to-Faceless.