The former academy player at Exeter moved to Pirates in the summer of 2013.
He led the club to their highest-ever league finish when they ended the 2023-24 season in second place in the Championship, seven points behind winners Ealing.
“He wasn’t the biggest when we first set eyes on him,” joint head coach Gavin Cattle said.
“Alan Paver and myself were still players back then, but as a coach to see him grow into a great captain that leads from the front has been a joy to watch.
“I don’t say this lightly but I feel he’s one of the best we have ever had.
“Injuries hampered his progress, but that’s rugby and to see him overcome an horrific injury to make his 150th appearance sums up what he’s about.
“John has been inspirational and he has put one hell of a shift in for this club.”
