George MacKay was born in 1992 in Hammersmith, London, England, to Kim Baker, a British costume designer, and Paul Christopher MacKay, an Australian stage/lighting manager, from Adelaide. His maternal grandmother hails from Cork, Ireland.
At the age of ten, George was scouted to audition for a role in the family feature, Peter Pan (2003). He landed the part of Curly, one of the Lost Boys, and went on to have several minor roles on TV, including an episode of Rose and Maloney (2002) and Footprints in the Snow (2005). By thirteen, George had already landed the part of Riccio in the film adaptation of Cornelia Funke's best-selling children's novel, The Thief Lord (2006),starring Aaron Taylor-Johnson, and was also cast in the lead role for the BBC adaptation of Terry Pratchett's Johnny and the Bomb (2006).
George worked with notable actors such as Tim Roth, Chiwetel Ejiofor, and Sophie Okonedo for the HBO Movie Tsunami: The Aftermath (2006) and later took a part in the Dickensian drama, The Old Curiosity Shop (2007). He co-starred with Daniel Craig and Liev Schreiber on Defiance (2008). In 2009, George took on the role of Harry in The Boys Are Back (2009) alongside Clive Owen, earning him two award nominations.
His career took another step forward with Hunky Dory (2011). Since then, George has featured in several shorts that have been popular on the festival circuit and played the part of Tommo Peaceful alongside Jack O'Connell in the adaptation of Michael Morpurgo's Private Peaceful (2012).
2013 was George's breakthrough year, and he was recognized for his roles as Aaron in For Those in Peril (2013),Davy in the musical Sunshine on Leith (2013),Jake Whittam in Breakfast with Jonny Wilkinson (2013),and the dark horse Eddie in How I Live Now (2013). He received several nominations and won a total of five awards for these features.
George had a stint in the West End in 2014 in The Cement Garden. He portrayed Joe in the well-received Pride (2014) and Duane Hopkins' Bypass (2014) premiered at the BFI London Film Festival in October. Both Captain Fantastic and Sadie Jones' The Outcast (2015) are in post-production, and George will be returning to theatre for Eugene O'Neill's 'Ah, Wilderness!' this April.
In 2016, George starred in the film Captain Fantastic (2016),opposite Viggo Mortensen, and the mini-series 11.22.63 (2016),with James Franco and Sarah Gadon. He rounded out the decade playing the starring role in Sam Mendes' 1917 (2019),a box office hit and highly critically-acclaimed drama set during World War I and shot to simulate a single take in real time.