Regbo started his acting career with a small role in 2006 ITV television film Sharpe's Challenge. In 2007, he played American teen spy Chad Turner in an episode of CBBC children's spy-fi adventure series M. I. High. He continued to pursue his acting career in 2009, when he played Michael Walton in Stephen Poliakoff's period drama Glorious 39. One of his most notable roles was in a science fiction drama Mr. Nobody, premiered in 2009. He played eponymous character Nemo Nobody (in his teenage years). He also played young Albus Dumbledore in the film Harry Potter and the Deathly Hallows – Part 1 and will reprise the role in the 2018 film Fantastic Beasts: The Crimes of Grindelwald. He made his stage début as Eliot in Tusk Tusk, a 2009 play by Polly Stenham, at the Royal Court Theatre in London. Regbo played James Sveck in the film version of Peter Cameron's novel Someday This Pain Will Be Useful To You, shot in the summer 2010 in New York. In 2013, Regbo played John in drama-thriller film uwantme2killhim? directed by Andrew Douglas and produced by Bryan Singer. He was originally cast in Disney's Maleficent as young Stefan, but was ultimately replaced by Michael Higgins as the directors decided they wanted a younger boy to play the part.