Thomas Mark Harmon was born on September 02, 1951 as youngest child of former actress Elyse Knox and her husband, former Michigan football player and Heisman Trophy winner, Tom Harmon.
After attending Harvard School, North Hollywood and Pierce Junior College he enrolled at UCLA. He joined the UCLA Bruins and was really successfull as their quarterback.
Mark Harmon finished UCLA with a degree in communications.
The marriage of his older sister Kristin to Ricky Nelson brought him his first acting job in an episode of "Ozzie's Girls"
After a few more guest appearances on several tv shows he played Robert Dunlap in "Eleanor & Franklin: The White House Years". The way he portrayed the wounded soldier was highly acclaimed by critics and got him his first Emmy Nomination.
Most people will remember his role Fielding Carlyle in the early 80ies soap opera "Flamingo Road" alongside household names like Morgan Fairchild, Kevin McCarthy and Barbara Rush.