In the former, he overcame Ian Black 5–0 and Ray Edmonds 5–2 before losing 1–5 to Tony Drago; the latter featured wins over Jim Chambers, Kirk Stevens and Bob Chaperon, but ended with a 1–5 defeat to Thorne.

At the 1989 International Open, Marshall reached the last-16 stage, defeating Paul Watchorn, Colin Roscoe, Dean Reynolds and Eddie Charlton before exiting 3–5 to Welshman Cliff Wilson.

He registered the best performance of his career at the 1990 British Open, where his opponents en route to the semi-final included Nigel Gilbert, David Roe, Joe Johnson, Eugene Hughes and Steve Newbury.

Ranked at a career-best 46th for the 1990/1991 season, Marshall defeated Tony Wilson of the Isle of Man, fellow Englishman Mark Johnston-Allen and South African Peter Francisco - all 10–9 - to qualify for the main stages of the 1991 World Championship, his first appearance at the Crucible Theatre.

He had made a break of 133 in his 1995 World Championship qualifying match against Kieran McMahon, but lost 4–5 to the Northern Irishman and did not play professionally again; he was relegated from the tour in 1996, aged 31.