A back row forward, Dun played for Bristol between 1980 and 1990, appearing in 170 senior matches, with two seasons as club captain.[2] While undergoing his medical training at St Bartholomew’s Hospital, Dun played for London club Wasps and stood in for Nigel Melville as club captain in the 1983-84 season.[3] He was a Middlesex county player and got capped once for England, against Wales at Twickenham during the 1984 Five Nations Championship.[4]
Dun is the father of Bristol Bears player James Dun.[5]