“Even when I used to come back here to play against Rovers, it was always nice to come back to The Mem. And it’s even better that I get to play for the gaffer again.
“We trust each other. He’s done a lot for my career. I give 100 per cent for him and I always have and always will. When he gave me the call about coming back to Rovers, it was an easy decision for me.”
Harrison also played for Portsmouth, Fleetwood and Port Vale – the latter also under Clarke. He was released by MK Dons in May after two seasons in which he make 59 appearances, scoring 12 goals.
He spent part of the last campaign on loan at Walsall, scoring three goals in 12 games.
Bristol Rovers director of football Ricky Martin said Harrison will be “valuable” for a team looking to improve in front of goal this season.
“His profile is a clear match for the type of player we were looking for to strengthen our attacking options and his goals and assists will be immensely valuable for the team this season,” he added.