Firth, who said he was “celebrating with my colleagues 3ft above the ground”, is joined on the list by supporting actor nominees Helena Bonham Carter and Geoffrey Rush.
The Oscars take place on 27 February.
Firth, nominated for his performance as the stammering King George VI, added: “Not used to this much joy or this much champagne at this hour.”
Co-star Rush – who won the best actor Oscar in 1996 for Shine – said it was “very exciting to have your work honoured by your industry peers”.
The Australian actor, who plays the king’s speech therapist, said the film had “struck such a rich resonant chord with audiences of all ages”.
His film faces strong competition for best movie from Golden Globe winner The Social Network, ballet thriller Black Swan and sci-fi epic Inception.
Debra Granik’s drama Winter’s Bone, True Grit, The Fighter, 127 Hours and Toy Story 3 are also contenders.
- The King’s Speech – 12
- True Grit – 10
- Inception – 8
- The Social Network – 8
- The Fighter – 7
- 127 Hours – 6
- Black Swan – 5
- Toy Story 3 – 5
- The Kids Are All Right – 4
- Winter’s Bone – 4
- Alice in Wonderland – 3
- Biutiful – 2
- Harry Potter and the Deathly Hallows Part 1 – 2
- How to Train Your Dragon – 2
For best actor, Firth goes up against Javier Bardem for Biutiful, Jeff Bridges for True Grit, and James Franco for Danny Boyle‘s rock-climbing film 127 Hours.
Jesse Eisenberg – who played Facebook founder Mark Zuckerberg in The Social Network – is also nominated.
In a statement, the star said: “To be nominated for this award, especially alongside these other actors, is truly astonishing and a great honour for me.”
Golden Globe winner Natalie Portman, for ballet thriller Black Swan, is up for best actress alongside Annette Bening, for gay parenting movie The Kids Are All Right, and Nicole Kidman, for Rabbit Hole.
Jennifer Lawrence is also nominated for Rabbit Hole while Michelle Williams is up for romantic drama Blue Valentine.
The supporting actress Oscar could prove the most competitive among the acting prizes.
Melissa Leo, who won the Globe for The Fighter, faces strong challenges from co-star Amy Adams while 14-year-old newcomer Steinfeld – who missed out on a Globe nomination for True Grit – has received a nod.
In a successful year for Britons, other nominees include Welsh-born Christian Bale – up for supporting actor for boxing film The Fighter – and director Mike Leigh, for his Another Year original screenplay.
Leigh said he was “thrilled to bits” with his seventh Oscar nomination.
Danny Boyle, who dominated the Oscars in 2009 with Slumdog Millionaire, is up for best adapted screenplay for 127 Hours.
Meanwhile, John Hawkes for Winter’s Bone, Jeremy Renner for The Town, and Mark Ruffalo for The Kids Are All Right complete the best supporting actor list.
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The King’s Speech leads the nominations
The directing category, won by Kathryn Bigelow for The Hurt Locker last year – a first for a woman – is all male this year.
The King’s Speech’s Tom Hooper competes with Darren Aronofsky for Black Swan, David O Russell for The Fighter, the Coen brothers for True Grit, and David Fincher for The Social Network.
Fincher said he was “very grateful and humbled” by his film’s nominations saying its success “belongs to many people”.
As well as best film, Toy Story 3 is named as a contender for best animation – as was Up last year.
The nominations were revealed by actress Mo’Nique and Academy president Tom Sherak.