Garfield beat both Firth's Oscar-tipped performance in The King's Speech and Riz Ahmed for his role in suicide bomber satire Four Lions.
In The Social Network the 27-year-old plays Facebook's co-creator Eduardo Saverin, while in Never Let Me Go he is the object of both Carey Mulligan and Keira Knightley's affections.
Accepting his award in a filmed message, he said: "I really, really appreciate it and intend to let this spur me and provide more fuel for my fire."
The actor is playing Spider-Man in a new film that focuses on the formative years of the comic book superhero, set for release in 2012.
Source: BBC
Hopefully his recorded acceptance video will be up on the internet soon!