As a child actor, McMullen made his television debut as Josh McLoughlin on the
Channel 4 soap opera
Brookside, playing the role from 2002 until the show's final episode in November 2003. In 2004, McMullen went on to appear as Timothy "Tigger" Johnson in the long-running
BBC One children's television serial,
Grange Hill. He was in an episode of the BBC One drama series
The Street, Next, he starred in
BBC Switch's
Proper Messy. He played half of a young gay couple who run away from their homes in an episode of the BBC One medical soap opera
Doctors (2006). On 4 June 2011 he appeared in the BBC One medical drama series
Casualty, as Ethan, the friend of a patient. On 27 December 2011, McMullen appeared in
Fast Freddie, The Widow and Me. in 2023, he starred alongside
Idris Elba,
Neil Maskell, and
Max Beesley for 7 episodes of the
Apple TV+ aeroplane drama series
Hijack (2023). In March 2025, he played the main role of Jamie Phelan, son of drug lord Ronnie Phelan (played by
Sean Bean), and Elaine Phelan (played by
Julie Graham), alongside
James Nelson-Joyce, in the
BBC One Liverpool based gangster television series,
This City Is Ours (2025). == Filmography ==