Pirkis was born in London on 6 January 1989. His mother is a publisher, and he has a sister. After being educated at Eton College, Pirkis began attending St Catharine's College, Cambridge, where he read Theology. There, he was captain of the college's football team in 2009.

Pirkis started his acting in school plays while attending Eton, though he never took them seriously. Although unsure what he wanted to do with his life, Pirkis was cast for his first professional role in 2003, when he appeared in the successful film, Master and Commander: The Far Side of the World. The hire occurred after production staff visited Eton to hire boys for the ship's teenage crew. Pirkis attended a workshop and auditions as "a joke", ultimately securing the part of the 13-year-old, eventually one-armed midshipman Lord Blakeney of HMS Surprise. Director Peter Weir thought Pirkis "stood out very early on, but not to the extent that you see in the film. That was a complete surprise." According to Pirkis, he was at first "nervous" about acting with Russell Crowe, but changed his mind when he realised that Crowe was "a pretty normal guy."

In 2005, Pirkis made his television debut. Until 2007, Pirkis played Gaius Octavian (later to become Caesar Augustus) in the BBC/HBO television series Rome. Many critics highlighted Pirkis and his character for praise. At the beginning of the first season, The Washington Post columnist Tom Shales remarked: "Played both knowingly and innocently by Max Pirkis, he gives the audience something it desperately needs... a character to root for, or at least care about." During the second series, Pirkis was replaced by Simon Woods in order for the show to depict an older version of the character.

Soon after being cast in Master and Commander, Pirkis was contracted to be represented by Hollywood talent agency ICM. The income he earned for the film was placed into a bank, making him wait until he turned eighteen. For his role, Pirkis received critical acclaim and won the Evening Standard British Film Award for Most Promising Newcomer and the Young Artist Award for Best International Performance by a Young Actor at the 25th Young Artist Awards. Pirkis was also nominated for Best Performance by a Youth in a Lead or Supporting Role – Male at the 4th Phoenix Film Critics Society Awards. Jeremiah Kipp of Slant Magazine praised Pirkis, writing that he "makes a winning impression as midshipman Lord Blakeney, a pugnacious one-armed lad who imitates the masculine bravado of Crowe and the bookish reserve of Bettany."