He was born Toby Finn Regbo in London, England. His father's family is of Norwegian origin. Regbo is a made-up name chosen by an ancestor to replace the common Norwegian name of Hanson, and Toby is related to all of the twenty or so Regbos that there are in the world, as of 2011. His maternal grandparents were an Italian cruise ship captain and an Australian ballerina, but his mother was born and brought up in London. He attended Latymer Upper School in West London. His interest in acting started with plays at school; later on, he attended the Young Blood Theatre Company.
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.In 2009, he played Michael Walton in Stephen Poliakoff's period drama Glorious 39.His biggest role to date was in a science fiction drama Mr. Nobody, premiered in 2009. He played eponymous character Nemo Nobody (in his teenage years). He played young Albus Dumbledore in the film Harry Potter and the Deathly Hallows – Part 1. 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.