In 1959, Mark made his film debut in The Journey, which starred Deborah Kerr, Yul Brynner and Jason Robards.

[5] He guest-starred in television programs including Have Gun – Will Travel, The Andy Griffith Show, My Three Sons, The Fugitive, Mission: Impossible, The Patty Duke Show, The Big Valley, My Favorite Martian, The Jack Benny Program, Bachelor Father and The Outer Limits.

[2] He played recurring roles such as Flip Rogers in Lassie and Steve Olson in Days of Our Lives.

[6] In 1962, Mark starred in the new CBS sitcom Fair Exchange, where he played the role of the son, Larry Walker.

[7] He appeared in films such as Safe at Home!, Marriage on the Rocks and Please Don't Eat the Daisies, the last as George Mackay.