The release date for the expected awards contender was postponed from Nov. 15 after Scorsese had trouble cutting the film's run time down from more than 180 minutes.
For weeks, the media speculated the film would be pushed back until 2014, so Scorsese could finish it.
But The Hollywood Reporter said Scorsese has successfully trimmed the movie to about 165 minutes and screened it for star Leonardo DiCaprio and Paramount executives.
The decision to release the film Dec. 25 -- in the heart of awards season -- was made late Monday, the entertainment industry trade newspaper said.
"Marty's work is fantastic. He's continued to work on it but now it's officially going to be ready for Christmas Day and I'm delighted," Paramount Chairman Brad Grey told The Hollywood Reporter.