Maguire had a strong start to the season, with wins including Joe Perry and Kyren Wilson, he reached the semi-final of the 2018 Riga Masters but lost 5–1 to Jack Lisowski. In October, Maguire advanced to another semi-final of a ranking event, but this time losing 6–3 to Stuart Bingham at the English Open. He performed fairly well at the 2018 UK Championship and progressed to the quarter final, but was beaten 6–1 by Mark Allen. After his strong performances for the past two seasons, Maguire returned to the Masters for the first time since the 2014/15 season; however, the opponent Mark Selby outscored him 712–190 and lost 6–2. Maguire reached his third semi-finals of the season at the German Masters in February, but was defeated by Kyren Wilson 6–1. At the World Snooker Championship, Maguire won both of his first two rounds in the decider against Tian Pengfei and James Cahill, but was unable to replicate the same feat against Judd Trump in the quarter final, losing 13–6.