Thomasin Katherin Helen Harcourt McKenzie (born 26 July 2000) is a New Zealand actress. After a minor role in The Hobbit: The Battle of Five Armies (2014), she rose to critical prominence after playing a young girl living in isolation in Debra Granik's drama film Leave No Trace (2018), winning the National Board of Review Award for Breakthrough Performance. She continued gaining recognition with supporting roles in the 2019 films The King, Jojo Rabbit, and True History of the Kelly Gang. In 2021, she starred in M. Night Shyamalan's thriller Old, Edgar Wright's psychological horror film Last Night in Soho, and Jane Campion's western film The Power of the Dog.