Born in New York to a Danish father and an American mother, Mortensen spent the early part of his childhood in Manhattan. His family traveled a great deal and he spent several years living in Venezuela, Argentina and Denmark. He began acting in New York, studying with Warren Robertson. He appeared in several plays and movies, and eventually moved to Los Angeles, where his performance in "Bent" at the Coast Playhouse earned him a Drama-logue Critic's Award. He is best known for his role in the Lord of the Rings Trilogy (Aragorn). He also has starred in two David Cronenberg films, the second, "Eastern Promises", earned him an Academy Award nomination for Best Actor.

Aside from acting and singing, Mortensen is also an accomplished poet, photographer and painter. He has released several albums of music and spoken word poetry, usually collaborating with guitarist Buckethead for these recordings. His press is called Perceval Press and can be found at http://www.percevalpress.com/ There you can buy both his work, as well as other artists work, including books of poetry, art, photography, essays, and musical CD's.