Began his career as a schoolboy with Peterborough United, making his debut against Shrewsbury as a 16 year old. Turning pro at 17 he was a regular member of the 'Posh' side and was attracting first division scouts.

At 18 Arsenal paid £50,000 to secure his services, and in three seasons at Highbury he made 25 appearances and scored one goal, making his debut against Birmingham City.

He also experienced European football with Arsenal, one of a very small number of past Aylesbury players to be able to make that claim.

In one such game against Red Star, Belgrade, the first leg was 1-2 to Red Star. In the second leg at Highbury, Arsenal were winning 1-0 (enough to take them through to the next round), the goal was made by Mark, when he was carried off injured with 5 minutes remaining. Before Arsenal could get their substitute on, the visitors had equalised to take the game.

He arrived at Northampton Town for £20,000 and was a regular member of their side making over 100 appearances in the first team.

In 1983 Northampton had a clear out and Heeley's contract wasn't renewed, making him free to move on to Aylesbury.