He took the final qualifying spot from the Pro Tour Order of Merit for the 2016 World Championship, but lost in the opening round for the sixth year in a row as he won just two legs during a 3–0 defeat to Jelle Klaasen. At the UK Open Cullen beat Mark Frost 9–1, Alan Norris 9–6 and Stephen Bunting 9–7 to play in his first major quarter-final. He produced a fightback from 9–3 down to Peter Wright, but would lose 10–7 with an average of 101.83, his highest in a televised match to date. This began a rich vein in form for Cullen as he reached the semi-finals of the first Players Championship event (lost 6–3 to Wright) and the same stage of the German Darts Masters (lost 6–1 to Michael van Gerwen after whitewashing reigning world champion Gary Anderson 6–0 in the quarters).