David Lilley's first big success was his victory at the Amateur European Championships in 1995, defeating his compatriot David Gray 8–7. In 1997 he reached the final of the English Amateur Championshipfor the first time and won it with a score of 8–7 against Robert Marshall. In 1999, he was by an 8–5 victory in the final against Andrew Norman English amateur champion. In the same year he reached the semifinals of the Amateur European Championships and the final of the World Amateur Snooker Championship, in which he defeated the Welshman Ian Preece 8–11. In 2000 he lost the final of the English Amateur Championship with 5–8 against Nick Marsh. In February 2002, he participated for the first time in qualifying for the World Snooker Championship, but retired in the second qualifying round against Timothy Paling. 2004 won Lilley by an 8–6 victory over Wayne Cooper for the third time the English Amateur Championship. In the 2004 World Amateur Snooker Championship he was narrowly defeated in the semi-finals 6–8 by the eventual champion Mark Allen. In qualifying for the 2005 World Snooker Championship, he retired in the third round against Stuart Mann. In the English Amateur Championship 2007, he lost in the final against Martin Gould only just with 7–8. After not having participated in international tournaments for seven years, he participated in the Players Tour Championship 2012/2013 – Event 2 in August 2012 and retired there in the first qualifying round against Ben Harrison. In May 2016, he tried to qualify for the Main Tour via Q School. In the first tournament he reached the final of his group, but lost there against the Chinese Chen Zhe, the second tournament he retired in the second round. Although he missed the qualification for the Main Tour, as seventeen of the Q-School Order of Merit he can participate as a substitute for tournaments of the season 2016/17. At the 2016 Indian Open, the second world ranking tournament of the season, he received for the first time a starting place. After defeating Tian Pengfei 4–3 in qualifying, he defeated Mike Dunn, Mark Williams and Robert Milkins in the main round to reach the quarter-finals, where he lost to England's Shaun Murphy 2–4. He was first on the Q School Order of Merit in 2018. He played very well in the 18/19 season, just missing out on gaining a tour card for the 19/20 season numerous times; he was 4th on the challenge tour list, and lost 5–4 to Kacper Filipiak in the 2019 EBSA European Snooker Championship, where a win would have granted him a place on the tour. He will appear in Snooker 19, making him the only player in the game who has never turned pro. On 23 May 2019, he beat Sean Maddocks 4–0 in the final qualifying round of Q School - Event 1, finally becoming a pro after 30 years as an amateur.
