This figure means the £6 million production, which stars David Jason and Marc Blake, has become the highest rated multichannel commission, beating BBC Three's Torchwood, which started on 2.4 million viewers in October.
2.4 million viewers initially tuned in to Sky One, according to unofficial overnights, but Hogfather increased its audience as Sky's multi-start viewers were added to the figures.
Sky One director of programmes Richard Woolfe said: "Sir David Jason has brought Christmas to Sky One early. Terry Pratchett's film was the perfect fantasy treat for people of all ages."
Only an episode of Friends broadcast on Sky One in January 2000, which was watched by 2.7 million viewers, has achieved higher ratings for non-sport content on the channel.