The film beat out "Amour," "Life of Pi," "Lincoln," "Beasts of the Southern Wild," "Silver Linings Playbook," "Django Unchained," "Zero Dark Thirty" and "Les Miserables" for the coveted statue -- the biggest award of the evening.
Affleck's co-producer Grant Heslov thanked his fellow co-producer George Clooney, and also thanked Affleck as a director -- a category in which he was not nominated.
Affleck himself thanked the people of Canada and Iran, and added, "I wanna thank my wife [actress Jennifer Garner], whom I don't normally associate with Iran -- but I want to thank you for working on our marriage," he said. "It is work, but it's the best kind of work, and there's no one I'd rather work with."
Affleck won his first Academy Award in 1997 for his screenplay for "Good Will Hunting." He has had an up-and-down career since, with "Argo" completing a comeback that began with "The Town." He acknowledged that in his speech.
"I was here 15 years ago or something, and I had no idea what I was doing . . . I was just a kid," he said. "I never thought that I would be back here, and I am -- because of so many of you who are here tonight. I want to thank them, and I want to thank what they taught me . . . which is, you have to work harder than you think you possibly can, and you can't hold grudges -- it's hard, but you can't hold grudges," he added to knowing laughter from the industry crowd.
Affleck finished up by saying, "It doesn't matter how you get knocked down in life, 'cause that's gonna happen. All that matters is that you've gotta get up."