He experienced early success with victories at the 1977 UK Championship and the 1977 Dry Blackthorn Cup but following a car accident, developed a psychological block when using the rest which affected his playing and he did not win another title.

He lost his professional status in 1989 following a 2–9 playoff defeat by Brady Gollan and now works as a snooker coach.

[4] He played at the Chiswick Memorial Club, and in 1974 it was reported in a local newspaper that in a six-frame session he had recorded a break of 106, another over 80, and three more over 70.

[6][7]: 122 [8] In 1975, Fagan became the youngest player ever to win the London and Home Counties billiards championship, playing with a focus on potting the red ball as he defeated Ron Riggins 1,176–881 in the final.

[11][2]: 39–40 In 1974, Fagan won a money match against Alex Higgins for £2,000,[12] an amount equal to that received by the winner of the 1974 World Snooker Championship.

[14] He made his first maximum break on 15 January 1977, his 26th birthday, against Dave Gilbert at the Clapton Bus Garage Social Club.

[2]: 39–40  At the 1977 World Snooker Championship, he beat Jim Meadowcroft 11–9 in qualifying and then lost 7–13 to defending champion Ray Reardon in the last 16,[1]: 58–59 [15] having finished the first session of the match level at 4–4 and the second 7–10 behind.

[18] The matches between Fagan and Reardon, and between Fred Davis and John Pulman, were the first to be held at the Crucible Theatre,[19] which as of 2022 had remained as the venue for the World Snooker Championship for 45 years.

He won in the deciding frame in each of the next two rounds, 5–4 against Jim Meadowcroft in the quarter-finals and 9–8 against John Virgo in the semi-finals, to reach the final against another player in his first year as a professional, Doug Mountjoy.

This version of the "yips" caused him to spend a long time cueing and then usually miscueing; because of this, he would play left-handed rather than using the rest where possible.

In their match against the Northern Ireland team, Fagan lost 0–1 to Dennis Taylor on the first day,[35] in a match where Taylor asked him to play again after Fagan had fouled by touching the blue ball with his sleeve whilst using the rest in attempting to hit the yellow ball.