He is known for his role as young Nemo Nobody in the science fiction drama Mr. Nobody (2009), as Francis II of France in Reign (2013–2017), Æthelred in The Last Kingdom (2017–2020), Tommaso Peruzzi in Medici: Masters of Florence (2019) and Jack Blackfriars on A Discovery of Witches (2022) and he starred in Platform 7 (2023).

[11][12][13][14] 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.

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.

Regbo was set to be part of the cast of the planned Game of Thrones prequel titled "Bloodmoon" but the pilot did not get picked up.

[13] Matt Wolf, writing for The New York Times, was also very complimentary about the pair, concluding: "... these newfound talents inhabit every mercurial point on a spectrum that makes them one another's protectors and their destroyers, enemies and allies.

produced by Bryan Singer, typically centered upon Regbo and his co-star Jamie Blackley's acting,[21] with the Screen Daily commenting that the two delivered "strong performances".

Variety praised his performance commenting "The impressive Regbo is on surer footing as a meek geek with some surreptitious social skills".