Sangster is also known for his role as Jojen Reed in Game of Thrones, his voice as Ferb Fletcher in Phineas and Ferb (including the one-hour special episode Phineas and Ferb: Star Wars), as John Tracy in the ITV series Thunderbirds Are Go, as well as his roles as Sam in Richard Curtis's Love Actually, mischievous Simon Brown in Nanny McPhee and Newt in the 2014 filmThe Maze Runner, the 2015 sequel, Maze Runner: The Scorch Trials and the 2018 final movie The Maze Runner: Death Cure. Sangster also grew in popularity for starring in critically acclaimed cult films such as Casey in Some Dogs Bite, Donald Clarke in Death of a Superhero, Samuel Brawne in Bright Star and Paul McCartney in Nowhere Boy.