The 37-year-old actor will star as Jim Shannon, a man from 2149 who travels through time with a group of settlers to set up a colony in prehistoric Earth in order to save the human race.
"Writing the character of Jim Shannon, we've thought of Jason O'Mara as something of an archetype," executive producer Brannon Braga told the trade paper. "He has an everyman quality to him, but there's something dangerous underneath."
O'Mara most recently starred in ABC's short-lived Life on Mars, in which he played a modern-day police detective who is transported back to the 1970s.
Terra Nova, also executive-produced by Steven Spielberg, is set to debut at midseason.
Will you watch Terra Nova?