The royal drama, about stuttering British monarch George VI, led the competition with 12 nominations going into this year's (11) Oscars, and edged out the likes of Black Swan, The Fighter, Inception and The Social Network to claim the most coveted title of the night.
Firth was crowned Best Actor in a Leading Role, emerging triumphant over Javier Bardem (Biutiful), Jeff Bridges (True Grit), Jesse Eisenberg (The Social Network) and James Franco (127 Hours).
Filmmaker Tom Hooper also basked in Oscar glory as he was hailed Best Director, beating Darren Aronofsky (Black Swan), David O. Russell (The Fighter), David Fincher (The Social Network) and Joel and Ethan Coen (True Grit).
Pregnant Natalie Portman fought back tears as she walked away with Best Actress in a Leading Role for her portrayal of a tormented ballet dancer in Black Swan, ahead of Annette Bening (The Kids Are All Right), Nicole Kidman (Rabbit Hole), Jennifer Lawrence (Winter's Bone) and Michelle Williams (Blue Valentine).
She gave special thanks to her Black Swan choreographer and fiance Benjamin Millepied, telling the audience, "So many people helped me prepare for this role... my beautiful love, Benjamin Millepied who choreographed the film and has now given me the most important role of my life."
It was also a golden night for The Fighter, about tough Boston, Massachusetts boxing legends Mickey Ward and Dickie Eklund, as Christian Bale and Melissa Leo dominated the Best Supporting categories.
Meanwhile, moviemaker Francis Ford Coppola, actor Eli Wallach and historian Kevin Brownlow were given a standing ovation in recognition of the lifetime achievement honours they received at the Academy of Motion Picture Arts and Sciences' Governors Awards in November (10). Fellow honouree Jean-Luc Godard did not attend the ceremony.
Oscars co-hosts Anne Hathaway and James Franco opened the 2011 Academy Awards with a hilarious spoof poking fun at the Best Picture nominees, while 2010 presenter Alec Baldwin and Morgan Freeman also made surprise appearances in the skit.
Gwyneth Paltrow, Mandy Moore and Zachary Levi, Randy Newman, and Florence Welch and A.R. Rahman provided the music for the night as they performed the tracks nominated for Best Original Song.
And Celine Dion took to the Kodak Theatre stage in Los Angeles to sing Smile during the ceremony's annual In Memorium segment, remembering the stars lost in the past 12 months, including Tony Curtis, Leslie Nielsen, Dennis Hopper, Pete Postlethwaite and Gloria Stuart.
The complete list of winners at the 83rd Annual Academy Awards is as follows:
The King's Speech
Best Actor in a Leading Role:
Colin Firth, The King's Speech
Best Actress in a Leading Role:
Natalie Portman, Black Swan
Best Actor in a Supporting Role:
Christian Bale, The Fighter
Best Actress in a Supporting Role:
Melissa Leo, The Fighter
Tom Hooper, The King's Speech
Best Screenplay - Adapted:
Aaron Sorkin, The Social Network
Best Screenplay - Original:
David Seidler, The King's Speech
Best Foreign Language Film:
In a Better World (Denmark)
Best Animated Feature:
Toy Story 3
Best Documentary (Feature):
Best Art Direction:
Robert Stromberg and Karen O'Hara, Alice In Wonderland
Wally Pfister, Inception
Best Sound Mixing:
Lora Hirschberg, Gary A. Rizzo and Ed Novick, Inception
Best Sound Editing:
Richard King, Inception
Best Original Score:
Trent Reznor and Atticus Ross, The Social Network
Best Original Song:
We Belong Together from Toy Story 3, Randy Newman
Colleen Atwood, Alice in Wonderland
Best Documentary (Short Subject):
Strangers No More
Best Film Editing:
The Social Network
Best Animated Short Film:
The Lost Thing
Best Live Action Short Film:
God of Love
Best Visual Effects: