He also starred as David in the thriller film The Guest (2014), Sir Lancelot in the adventure film Night at the Museum: Secret of the Tomb (2014), The Beast/Prince in Disney's live action adaptation of Beauty and the Beast (2017), Lorin Willis in the biographical legal drama Marshall (2017), Charles Dickens in the biographical drama The Man Who Invented Christmas (2017) and Russian Eurovision singer Alexander Lemtov in Eurovision Song Contest: The Story of Fire Saga (2020).

His debut performance earned him glowing reviews from prominent critics in Britain and the United States,[11][12][13][14] as well as a commendation at the 2004 Ian Charleson Awards.

[17] In 2008, Stevens appeared in the BBC adaptation of Jane Austen's novel, Sense & Sensibility, playing Edward Ferrars, and the West End revival of Noël Coward's The Vortex.

[19] In June 2009, he returned to the West End, playing Septimus Hodge in an acclaimed revival of Tom Stoppard's Arcadia at the Duke of York's Theatre.

[20] In 2010, Stevens got his biggest break[21] when he was cast as Matthew Crawley in the ITV series Downton Abbey, created and written by Oscar-winning[22] screenwriter Julian Fellowes.

[25][26] His exit caused a huge uproar with fans, who notably took to Twitter and other social media sites to express their anger at the character's death.

In March 2012, he completed shooting Vamps, from Amy Heckerling, and Summer in February, an Edwardian romance film set in an artist colony.

[28] Also in 2012, Stevens moved with his family to New York City,[29] when he made his Broadway debut that year opposite Jessica Chastain and David Strathairn in The Heiress.

[30] In 2014, Stevens starred in the independent film The Guest, winning critical acclaim for his portrayal of a recently discharged army veteran who goes on a killing spree to protect his true identity.

[34][35][36][37] In February 2016, Stevens was cast in the lead role of David Charles Haller in the FX series Legion, an X-Men-related drama created by Noah Hawley and he also starred alongside Anne Hathaway and Jason Sudeikis, giving life to Tim, Gloria's ex-boyfriend, in Colossal.

[42][43][44] At the same year, he appeared in Marshall with Chadwick Boseman, Josh Gad and Kate Hudson,[45] and The Man Who Invented Christmas, directed by Bharat Nalluri, and co-starring Christopher Plummer and Jonathan Pryce.

[50] The same year, he appears as an "absurdly lascivious" Russian crooner in the Netflix musical comedy film Eurovision Song Contest: The Story of Fire Saga, co-starring with Will Ferrell and Rachel McAdams.

That same year he also played a leading role as the veterinarian Trapper in Godzilla x Kong: The New Empire with Rebecca Hall and Brian Tyree Henry, directed by Adam Wingard.

He has upcoming roles in biographical drama Swiped with Lily James, horror film The Ritual with Al Pacino, and as lead actor and executive producer of the third season of The Terror, adapting Victor LaValle's novel The Devil in Silver, for AMC.