Mc Avoy assessed his character to be a "completely selfish prick".The breakthrough role in Mc Avoy's career came in Atonement, Joe Wright's 2007 adaption of Ian Mc Ewan's novel of the same title.This was followed by a supporting role, the faun Mr.Tumnus, in The Chronicles of Narnia: The Lion, the Witch and the Wardrobe (2005).Mc Avoy's mother suffered from poor health and subsequently decided it was best that he live with his maternal grandparents, Mary and James Johnstone, a butcher who lived in a terraced council house in the nearby Drumchapel area of Glasgow.Mc Avoy's acting debut came at the age of 15 in The Near Room (1995).More cable work came for him when he accepted the role of an unprincipled reporter in 2003's State of Play.
He also shared that he hoped viewers will be left "absolutely devastated and harrowed." Screenings of Atonement were held at the 2007 Toronto International Film Festival, where it was one of the most acclaimed films present, and Venice Film Festival.
He later admitted that he was not very interested in acting when joining the film, but was inspired to study the acting after developing feelings for his co-star, Alana Brady.
Throughout the early 2000s, he made guest appearances in television shows and began working on movies.
That succeeding year he also accepted the principal role of Brian Jackson, a nerdy university student who wins a place on a University Challenge quiz team in the mid-1980s, in Starter for 10.
He was directed by David Nicholls, who adapted the film's screenplay from his own book.
His public profile was raised in 2005 with the release of Walt Disney Pictures's The Chronicles of Narnia: The Lion, the Witch and the Wardrobe.