He reached the final of the PDPA World Championship Qualifier, where he was beaten 5–3 by Arron Monk. The result meant that he qualified for the preliminary round of the 2012 World Championship, where he beat Oliver Ferenc of Serbia by 4 legs to 2. He played number 10 seed Terry Jenkins in the first round for the second successive year and was beaten 3–0, winning just three legs in the match. In April, he earned a place in the Austrian Darts Open by defeating Sam Hill and John Bowles in the UK qualifier. He played Brendan Dolan in the first round and won 6–4, and then continued his run by beating Simon Whitlock 6–4, despite his opponent hitting a nine darter. Cullen defeated Mark Walsh to make the quarter-finals, where he was this time on the wrong end of a 6–4 scoreline as he lost to eventual winner Justin Pipe. Cullen's best result of the season came a week after this as he won through to the semi-finals of the final UK Open Qualifier, but was then whitewashed 6–0 by Pipe. He also qualified for the third European Tour event, the European Darts Open and beat Jenkins 6–1 in the first round in Düsseldorf, before losing to Johnny Haines 6–5 in round two.