Prior to pursuing a career as an actor, Hagan planned to study accountancy at Northumbria University and join his father's business[citation needed].
Hagan's first notable role after drama school was a part as Vito Barratini, a muse of the artist Michelangelo, in Antony Sher's play The Giant.
He has also taken his turn in several productions for the Royal Shakespeare Company, including roles in Twelfth Night, The Tempest, The Comedy of Errors and Troilus and Cressida.
Other roles have included Shooting for Socrates, Best: His Mother's Son, Risen (as Bartholemew) with Joseph Fiennes, Zoo and A Royal Christmas with Jane Seymour.
The two had met ten years prior to the show, when Hagan was a teenager and Nesbitt was back in Northern Ireland filming Murphy's Law.