The recognition at the film industry’s top honours will likely boost cinema, DVD, and digital sales for the film, which has collected €70m at global box offices.
It was the second best-picture trophy in a row for Fox Searchlight after last year’s victory for 12 Years a Slave.
The studio also scored with offbeat winner The Grand Budapest Hotel, which took four trophies in technical categories.
Movie studios mount months-long, multimillion- dollar campaigns for Oscar trophies to earn prestige, grab bragging rights they can use in advertising, and kickstart ticket or home entertainment sales.
Birdman is a surreal story about a washed-up movie star trying to rebuild his career with a stint on Broadway. It was filmed in an unusual style in what seems like one long, continuous take featuring an avian alter-ego with a booming voice.
“Everything sounds so risky,” said Mexican director Alejandro Inarritu backstage after the awards. “Fox Searchlight, they are smart guys. They trusted me. It could have been a disaster.”
The post-Oscar bump for each of the last five best picture winners has translated into millions of dollars at the box office, said Keith Simanton, managing editor of movie website IMDB.
Birdman prevailed in what many Oscar watchers called a two-way contest with coming-of-age tale Boyhood from small distributor IFC Films, a unit of AMC Networks Inc. Boyhood ended the night with one trophy for best supporting actress Patricia Arquette.
IFC Films was new to the best-picture race. The New York-based distributor abandoned most film production about a decade ago but stuck with Boyhood, which was filmed for a few weeks each year for 12 years, using the same cast.
Sony’s movie studio, hit by a devastating cyber attack in December, earned four awards including best supporting actor for JK Simmons in Whiplash and best actress for Julianne Moore in Still Alice.
Another best picture contender, American Sniper from Warner Bros, grabbed only one Oscar, for sound editing. But it is far ahead of fellow nominees at the box office, having collected more than $428m worldwide.
Disney won the animated feature for a second year in a row, this time with Big Hero 6 about an inflatable oversized waddling robot.