"A writer is only as good as people he works with," said screenwriter Michael Arndt during his acceptance speech.
He thanked the cast who "collectively saved my life."
William Monahan, who based Boston mobsters in "The Departed" on the Hong Kong film "Infernal Affairs," won the Academy Award for adapted screenplay.
He said the movie that drew him to his craft was "Lawrence of Arabia," starring Peter O'Toole.
"I don't know what happened in the universe for me to end up here tonight with Peter O'Toole," he said.
O'Toole is on hand as a nominee for best actor in "Venus."
Monahan said people working on "The Departed" were "on the top of their game before they started. Under (Martin Scorsese's) direction, it only got higher after that."