Solomon Northup (played by Ejiofor) was a free man who was abducted and sold into slavery.
The harrowing drama 12 Years a Slave won the Best Film award at Britain's top movie honours on Sunday, cementing its status as favourite for the Oscars next month, but it was the space thriller Gravity that claimed the biggest trophy haul.
Here is a list of winners in the main categories at the 2014 BAFTAs, Britain's top film honours:
BEST FILM: 12 Years a Slave
OUTSTANDING BRITISH FILM: Gravity
BEST DIRECTOR: Alfonso Cuaron for Gravity
LEADING ACTOR: Chiwetel Ejiofor in 12 Years a Slave
LEADING ACTRESS: Cate Blanchett in Blue Jasmine
SUPPORTING ACTOR: Barkhad Abdi in Captain Phillips
SUPPORTING ACTRESS: Jennifer Lawrence in American Hustle
DOCUMENTARY: The Act of Killing
ANIMATED FILM: Frozen
ORIGINAL SCREENPLAY: Eric Warren Singer and David O. Russell for American Hustle
ADAPTED SCREENPLAY: Steve Coogan and Jeff Pope for Philomena
FILM NOT IN THE ENGLISH LANGUAGE: The Great Beauty
ORIGINAL MUSIC: Gravity