Mark was born on May 30, 1964, in London, England, into the family of the famous actor William Morgan Sheppard, and later followed in his footsteps and became an actor. Mark first appeared on screen in the series "Silk Stalkings," where he played small roles in two episodes. The real breakthrough in the film industry came after his role in the film "In the Name of the Father," because after that he began appearing in such popular series as "Charmed," "The X-Files," and "Soldier of Fortune" (one of the main roles), but one of Mark's most memorable roles is precisely the demon Crowley.

In 2004, Mark married Jessica Mark, and they had two sons: Maximilian and William. In December 2014, they separated. He is currently engaged to Sarah Fudge, who announced on her Twitter on September 26, 2015, that she was pregnant. On March 1, 2016, the couple had a daughter, Isabella Rose Sheppard.