Moments earlier, the French movie's star, Jean Dujardin, collected the Best Actor statuette, exclaiming: "Thank you! I love your country!"
The Best Director trophy went to "The Artist" director Michel Hazanavicius.
"I have an Oscar," he declared. "I forgot my speech. I am the happiest director in the world right now. Thank you for that."
The film also scored the awards for Best Costume Design and Best Original Score
The absent Woody Allen won the Oscar for Best Original Screenplay for "Midnight in Paris," while Alexander Payne, Nat Faxon and Jim Rash took home the prize for Best Adapted Screenplay for "The Descendants."
"We bow to our fellow nominees," Payne said. "We share this with George Clooney and the rest of the cast for interpreting our screenplay so generously. We also share it with, particularly, Kaui Hart Hemmings, a beautiful Hawaiian flower, for her novel."
Payne then dedicated his win to his mother, who was sitting in the audience.
"Thanks for letting me skip nursery school so we could go to the movies," he told her.
Meryl Streep won the Best Actress Oscar for her work in "The Iron Lady," Christopher Plummer picked up the Best Supporting Actor honor for his performance in "Beginners" and Octavia Spencer was presented with the Best Supporting Actress accolade for her turn in "The Help."
"Thank you, Academy, for putting me with the hottest guy in the room," Spencer joked, referring to her statuette.
She then expressed her gratitude to her loved ones, including her "'Help' family."
"Thank you, world," she said tearfully.