Raymond Plouhar, 30, was "conducting combat operations" in the country's restive western Anbar province when the device exploded, the US defence department said.
Although Plouhar willingly appeared in a segment of the 2004 film as a recruiter for the US marines, his father, Raymond, said on Tuesday that his son didn't realise that it was for a film that would be against the war.
"I'm devastated, sad and proud," Plouhar said of his only son.
"This just makes me devoted even more to his belief that people need help in Iraq, and he felt that he was helping."
Plouhar had only 38 days left in Iraq and had been there a little more than four months during his most recent tour, his family said.
Moore's controversial 2004 documentary, which condemned the Bush administration for its war on terror, featured Plouhar in several scenes when he worked as a recruiter for the US marines.
The documentary won the Palme D'Or at the Cannes film festival in 2004.