"I have a feeling my career's just peaked," Firth said after winning an Oscar in the best actor category. "I'm afraid I have to warn you that I'm experiencing stirrings somewhere in the upper abdominals which are threatening to form themselves into dance moves."
Natalie Portman's role as a delusional ballerina earned her the best-actress prize. It was Portman's first win in two nominations and follows her supporting actress nomination for "Closer," which was made in 2004.
"Thank you so much. This is insane, and I truly, sincerely wish that the prize tonight was to get to work with my fellow nominees. I'm so in awe of you," Portman said.
Among those Portman beat was Annette Bening for "The Kids Are All Right." Bening now has lost all four times she's been nominated.
Christian Bale and Melissa Leo both won their first Academy Award for their supporting role in "The Fighter."
"Fighter" co-star Amy Adams, who was also nominated for best supporting actress, said Leo deserved to win.
"I saw her work first hand, and she's remarkable," Adams said.
Leo had to be bleeped for saying the F-word during her acceptance speech. Backstage at the Kodak Theatre, Leo jokingly conceded it was "probably a very inappropriate place to use that particular word."
During Bale's acceptance speech, he joked that he was keeping his language clean.
"I'm not going to drop the F-bomb like she did," Bale said. "I've done that plenty of times before."
The 83rd annual Academy Awards kicked off with a comedic montage of scenes from the best picture-nominated movies, with co-hosts Anne Hathaway and James Franco inserted in each scene.
Hathaway arrived on the red carpet in a bold, red strapless Valentino gown, but when the show began, she had several costume changes, including a tuxedo, which prompted Franco to put on a blonde wig and a dress.
At 28, Hathaway was the youngest to ever host the Oscars.
The Associated Press contributed to this story.