Ejiofor began acting in school plays at his junior school, Dulwich Prep London (known at the time as 'Dulwich College Preparatory School'), where he played the gravedigger in William Shakespeare's Hamlet.
He continued acting at his senior school, Dulwich College and joined the National Youth Theatre.
He got into the London Academy of Music and Dramatic Art but left after his first year, after being cast in Steven Spielberg's film Amistad.
He played the title role in Othello at the Bloomsbury Theatre in September 1995, and again at the Theatre Royal, Glasgow in 1996, when he starred opposite Rachael Stirling as Desdemona.
In 1999, he appeared in the British film G: MT – Greenwich Mean Time.
Ejiofor portrayed the characters Okwe in Dirty Pretty Things (2002), The Operative in Serenity (2005), Solomon Northup in 12 Years a Slave (2013), Dr.
He played CIA officer Darryl Peabody in Salt (2010), and the Golden Globe Award-nominated leading role of band creator Louis Lester on the BBC Two drama series Dancing on the Edge (2013), which played on Starz in the United States.
In 2013, Ejiofor took on the role of Solomon Northup in 12 Years a Slave.
Ejiofor has received numerous awards and nominations for acting, including the BAFTA Orange Rising Star Award in 2006, two Golden Globe Award nominations, and the Laurence Olivier Award for Best Actor for his performance in Othello in 2008.
In 2008, he was appointed Officer of the Order of the British Empire by Queen Elizabeth II for services to the arts.
He also received acclaim for his performance as a complex antagonist The Operative in the film Serenity (2005). He was also nominated for the BAFTA Orange Rising Star Award in 2006, which recognises emerging British film talent.