McAuliffe is a native of the Sydney suburb of Clontarf, New South Wales. He is the son of Claudia Keech and Roger McAuliffe, who is a novelist, journalist, and director of Creative Writer. His cousin is actress Jacinta John. His grandparents were Irish. He attended The Scots College, an all-boy day and boarding school. He was the head chorister at the school. He was first noticed to have a natural talent when he topped the London Trinity College Musical Theatre Exams two years in a row and subsequently was invited to perform for the Australian Conservatorium. He was a track athlete until he got injured, leading him to a stronger focus on the performing arts. McAuliffe started acting at the age of 8, appeared in the local Australian TV series Comedy Inc. and Blue Water High, and had a recurring role on Packed to the Rafters. He starred in the Australian independent coming-of-age short film, "Franswa Sharl", in 2009 and had a role in Resistance, a U.S./Australian feature film, that year. McAuliffe made his American feature debut in the Warner Bros. film, Flipped, directed by Rob Reiner. He auditioned for the film while on vacation in the United States and won the role of Bryce, the romantic lead. The film is based on the 2001 novel of the same title by Wendelin Van Draanen.
In May 2010, McAuliffe was cast in a lead role in the science fiction film, I Am Number Four based on the novel of the same title by Pittacus Lore, the film is produced by Michael Bay. He played Sam, the best friend of Alex Pettyfer's title character, Number Four.
McAuliffe appeared as young Gatsby in the 2013 film adaptation of The Great Gatsby, directed by Baz Luhrmann; Leonardo DiCaprio played the older version of Gatsby.
McAuliffe was cast as the archangel Uriel alongside Djimon Hounsou in Alex Proyas' action film, Paradise Lost, before the project was suspended. In 2012, he starred in the Australian television Movie, Underground: The Julian Assange Story, as one of the teenage Assange's friends involved in the International Subversives. In 3 February 2013, Variety had announced that Callan will play alongside Samuel L. Jackson and India Eisley in the live-action movie remake of 1998 Japanese anime film Kite. Filming began on 26 February 2013 in South Africa.