A Great Britain international representative prop, he played for English clubs St Helens, Wigan, Widnes, Salford and Workington Town as well as in New Zealand for the Auckland Warriors.
Platt played loose forward in St. Helens' 15-14 victory over Leeds in the 1987–88 John Player Special Trophy Final during the 1987–88 season at Central Park, Wigan on Saturday 9 January 1988.
During the 1991–92 Rugby Football League season, Platt played for defending champions Wigan at prop forward in their 1991 World Club Challenge victory against the visiting Penrith.
During the 1992–93 Rugby Football League season Platt played at prop forward for defending RFL champions Wigan in the 1992 World Club Challenge against the visiting Brisbane Broncos.
In 1994 Platt signed with the new Auckland Warriors franchise of the Australian Rugby League, following John Monie, Dean Bell, Denis Betts and Frano Botica, but did not appear in the club's first ever game due to a knee injury.