Cullen first drove in the British Formula Ford in 2012 as a novice driver which means a driver has no race experience as stated in the MSA regulations, placing sixth overall in the standings and obtaining three podium positions. After partaking in the post-season GP3 test, Cullen signed with Marussia Manor Racing to compete in the GP3 Series in 2013.[3] He failed to score points all year, finishing 29th in the standings, having been beaten by both teammates in all qualifying sessions and races where each driver was classified.[4][5] During the winter, Cullen drove in the MRF Challenge Formula 2000 Championship and finished sixth overall.
He stayed with Marussia Manor for the 2014 GP3 season.[6] Following seven scoreless weekends from Cullen, the team withdrew due to financial troubles, meaning that Cullen would miss the round at Sochi.[7] He returned for the season finale with Trident Racing, but was unable to prevent himself from going a second successive season without scoring.[8] Cullen drove for Koiranen GP during the post-season test.
Cullen went back to the MRF series for 2014/2015, where he finished second with three victories, which turned out to be his only race wins in single-seaters.
After finishing third in the Porsche GT3 Cup Challenge Middle East during the off-season, the Irishman returned to the Porsche Supercup with Lechner Racing whilst also competing in the Porsche Carrera Cup Germany at Konrad Motorsport. In the latter, Cullen finished tenth in the standings, being beaten by all full-time drivers, meanwhile he classified 11th in the Supercup with a best result of seventh at the Red Bull Ring.[9]
For his third season in the Porsche world, Cullen remained with Lechner in the Supercup, but switched to Huber Racing in the PCCG.[10] He would end up 11th again in the former, whilst improving to ninth place in the latter's standings.
Cullen underwent another patchy season during 2021, as he raced in two events of the FIA World Endurance Championship with Risi Competizione, which included another appearance in Le Mans - where he and his teammates retired due to engine troubles.[18]
The following year saw the Irishman step into the WEC for the entire season, as he drove with new team Vector Sport in the LMP2 category.[19] Despite scoring a podium at Monza, Cullen and the team struggled, ending up tenth and second-lowest of the Pro class entries in the standings.[20][21]
Returning for the team's second season in the category, Cullen partnered Gabriel Aubry as well as fellow silver-ranked driver Matthias Kaiser for the 2023 WEC season.[22] With numerous technical issues and a collision at Monza, Vector Sport finished tenth overall, once again ranking second-lowest. However, a strong drive by Aubry carried the team towards a seventh place in class at Le Mans.[23][24]
Personal life
Cullen was born to an Irish father and a Cypriot mother.[25] He was coached by Adam Carroll during his early years in car racing.[12]