Born in Portadown, Northern Ireland, Luke represented local youth teams Loughgall Youth and Dungannon Swifts as a child. A clear talent, McCullough made his IFA Premiership debut at just fifteen, catching the attention of various clubs.
One of those clubs was English giants Manchester United, for whom he signed in July 2010, joining the academy system at Old Trafford.
Whilst in the academy system, Luke became a prominent member of various teams, captaining the academy side during the 2012-13 campaign, where he made 25 appearances. He joined League Two side Cheltenham Town on a one-month loan in January 2013, making just 1 appearance for the Robins — a 1-1 draw with Aldershot Town on 16th February 2013.
He was released from United at the end of the 2012-13 season, when he was signed by then Championship Doncaster Rovers after a successful trial. Following 15 appearances that campaign, and Doncaster's relegation to League One, McCullough became a regular in the side, playing 41 and 35 appearances in 2014-15 and 2015-16 respectively. He played 7 times in the 2016-17 season as Rovers secured an immediate return to League One following relegation to League Two in 2016, winning automatic promotion as the third-placed side.
The next two seasons were beset with serious injuries and Luke made just 14 appearances over those two campaigns, but at just twenty-four years old he had plenty of time to further his career statistics.
McCullough joined Tranmere on loan on 20th August 2018, signing a deal to keep him at Prenton Park until January 2019.
He brought with him a wealth of experience, both domestic and international, having also made 32 appearances for Northern Ireland across various age groups. He has been named in the senior squad on numerous occasions and has represented his country as a full international 6 times to date.
Luke made a huge contribution to Tranmere's 2018-19 promotion, playing 38 games for the SWA on the road to winning the 2018-19 League Two play-offs by beating Newport County at Wembley. Unfortunately, Luke sustained a season-ending injury towards the end of the campaign, and he remained injured until the new year.
During the interim, McCullough became a free agent, training with Rovers throughout his recovery before re-signing at Prenton Park on non-contract terms on 6th January 2020.
Interesting Fact: Luke was a member of the Northern Ireland squad that reached the round of sixteen at the 2016 European Championships in France.