12 Years a Slave came away with the big award of the night in one of the most hotly contested competitions of recent years.
Director Steve McQueen thanked his wife, who first showed him a copy of the original book, for "unearthing this treasure" and his parents before dedicating the win to "everyone who has endured slavery and 21 million who still do today".
Lupita Nyong'o won the best supporting actress prize for her role.
Lupita Nyong'o
The Mexico-born star, who is of Kenyan descent, thanked her co-stars Chiwetel Ejiofor and Michael Fassbender and said making the film and seeing the attention it has received was the "joy of her life".
Matthew McConaughey was named as best actor for his role in Dallas Buyers Club.
His co-star Jared Leto won the first award of the night after being named best supporting actor.
Jared Leto
The star beat Bradley Cooper, Michael Fassbender, Jonah Hill and Barkhad Abdi after playing an HIV-positive transgender woman in the film. Gravity was the other big winner at this year's awards, winning seven trophies, including best director for Alfonso Cuaron.
The film, starring George Clooney and Sandra Bullock, won in many of the technical categories.
Australian actress Cate Blanchett won the best actress prize for her role in Blue Jasmine, beating Sandra Bullock, Amy Adams, Dame Judi Dench and Meryl Streep.
Accepting her award, she praised her fellow actresses including the "sublime" Sally Hawkins and said films with strong female characters were not "niche".
Cate Blanchett
She said: "Audiences want to see them and in fact they earn money."
Earlier Hollywood stars arrived on the red carpet at the Dolby Theatre for the event which is being hosted by comedian Ellen DeGeneres.
She opened the show with a string of gags poking fun at the event.
She said: "For those of you around the world who are watching it has been a tough couple of days - it has been raining. We're fine, thank you for your prayers."
A selfie taken on DeGeneres' phone featuring Meryl Streep, Brad Pitt, Bradley Cooper and Jennifer Lawrence has become the most retweeted tweet in Twitter's history garnering over one million in just 45 minutes.
If only Bradley's arm was longer. Best photo ever. #oscars pic.twitter.com/C9U5NOtGap
— Ellen DeGeneres (@TheEllenShow) March 3, 2014
DeGeneres said: "We have broken Twitter."
Pharrell Williams was first to act to perform at the event, singing Happy from Despicable Me 2. They were followed by Karen O, U2 and Pink.
Williams, Karen O and U2 lost out in the original song category to Let It Go from Frozen. The box office hit also won the best animation prize.
Actor Benedict Cumberbatch photobombed U2 as they posed for a photo on the red carpet ahead of their touching Oscars performance of Ordinary Love.
Bette Midler received a standing ovation after singing The Wind Beneath My Wings following a montage paying tribute to members of the film industry who have died in the last year.
After joking about how hungry stars get during the notoriously long ceremony, DeGeneres appeared to order pizza which she then handed out to Leto and others sitting in the first few rows.
The award for best documentary short went to The Lady in Number 6: Music Saved My Life - a week after its inspiration, pianist and world's oldest Holocaust survivor, Alice Herz-Sommer, 110, died in London.
Italian film The Great Beauty won best foreign film while 20 Feet From Stardom was named best documentary, beating The Act Of Killing which had been a favourite to win.
The Great Gatsby won best costume and production design while the make-up and hairstyling award went to Dallas Buyers Club.
Although Jennifer Lawrence didn't win an Oscar this year, she did mange to steal the limelight when she tripped and fell at the ceremony fr the second consecutive year:
Away from the red carpet there's already been one Irish success story.
Dublin-based beauty brand 'Cocoa Brown' were chosen to supply fake tans to A-listers before last night's ceremony.
Academy organisers offered the company a spot in the famous 'pamper suite', where attendees added the finishing touches to their appearances.
Cocoa Brown was set up just over a year ago by Marisa Carter and post-Oscar sales are expected to soar.
Mail on Sunday journalist Alexandra Ryan is in LA and says the company is starting to get celebrity endorsements:
