McArdle was born in Glasgow, growing up in the city's Darnley neighbourhood[2] and attending St Ninian's High School, Giffnock.

[4][5] Having worked as a child actor in films, at 17 he made the decision to travel by bus to London to train as a professional without informing his parents;[2] he was accepted to RADA after initially fluffing his audition lines but managing to return and impress the selectors.

[6][3] He left the course towards its end in 2010, and in the same year he appeared in Macbeth at The Globe and starred in the summer smash hit Spur of the Moment by Anya Reiss at the Royal Court Theatre in London.

In 2012, he starred as Harold Abrahams in Chariots of Fire, Mike Bartlett's stage adaptation of the film of the same title, which opened at London's Hampstead Theatre on 9 May and transferred to the West End on 23 June, running through to 5 January 2013.

[8][9] In March 2018 he stayed with the production when it transferred to Broadway for an 18-week engagement at the Neil Simon Theatre and was nominated for the Drama Desk Award for Outstanding Actor in a Play.