Ejiofor, 36, plays black New Yorker Northup, who is kidnapped and sold into the American South slave trade in 1841.
The actor, a former EE Rising Star nominee, beat competition from Leonardo DiCaprio, who plays Jordan Belfort in The Wolf of Wall Street, Christian Bale for American Hustle, Bruce Dern for Nebraskaand Tom Hanks for Philomena.
Ejiofor thanked Bafta for the “incredible” award and paid tribute to McQueen’s “artistry and passion”.
“You really brought us all through it,” he told the director. “You had the real vision to tell this remarkable story. The extraordinary life that he had, and to tell this story in a way to make it of such value, of such worth to all who were there. Thank you for this, it was yours. I’m going to keep it, but it’s yours.”
Ejiofor originally turned down the role of Solomon Northup out of fear of being “the guy that messed it up”.