Smit-McPhee was born on 13 June 1996[1] in Adelaide, South Australia, the son of Sonja Smit and Andy McPhee. His father is an actor and former professional wrestler. His older sister is actress and singer Sianoa Smit-McPhee.[2]
At age 16, Smit-McPhee was diagnosed with ankylosing spondylitis, a degenerative form of arthritis which causes vertebrae in the spine to fuse and can lead to chronic pain and loss of vision.[3][4] While filming The Power of the Dog, his vision was impaired in his left eye due to a severe cataract related to his condition.[5]
Smit-McPhee's first feature film role was in Romulus, My Father, which garnered him the 2007 AFI Award for Best Young Actor[6] as well as a Best Actor nomination.[7] For his appearance in The Road (2009), he received a Critics' Choice Award nomination for Best Young Actor[8] and a 2010 Australian Film Institute (AFI) nomination for Best International Actor.[9] The following year, he starred in Let Me In, for which he received a 2010 Critics Choice Award nomination for Best Young Actor for his performance in the film.[10]
In 2013, Smit-McPhee filmed the action science fiction film Young Ones. The film premiered at the Sundance Film Festival in January 2014. Soon afterwards he appeared in Slow West, which was released in 2015.[12]
In March 2014, he was cast in the Nine Network's seven-part drama series Gallipoli which was broadcast in February and March 2015, the year that marks the 100th anniversary of the Gallipoli landing. He plays 17-year-old Thomas "Tolly" Johnson, who pretends to be older so that he can enlist with his brother Bevan and ends up fighting at Gallipoli in the campaign that helped create the Anzac legend.[13] Aged 17 when he undertook the role, Smit-McPhee said afterwards that it showed "that soldiers aren't the patriotic brave souls they look like, it's showing them at their most vulnerable in tragic times and when they are terrified".[14]