Like most people I can be lazy, so it's nice to have a goal or deadline or reason to work out. I feel better when I get to exercise, or when I'm outdoors. I like to hike, swim and run, and I love to play soccer.

In the The Two Towers DVD extras the film's swordmaster Bob Anderson described Mortensen as "the best swordsman I've ever trained. They're accompanied by pictures of landscapes taken during the previous two winters. Mortensen also talked about his work with Bob Anderson the swordmaster on The Lord of the Rings Alatriste Pirates of the Caribbean and many others.

He campaigned for Dennis Kucinich in the 2008 United States presidential election and later endorsed Barack Obama for President. He made his film debut in Peter Weir's 1985 thriller Witness and subsequently appeared in many notable films of the 1990s including The Indian Runner (1991) Carlito's Way (1993) Crimson Tide (1995) Daylight (1996) The Portrait of a Lady (1996) G. Mortensen is politically active.