Marwood, who has been at the helm of Spar UK for almost nine years, will leave next summer to "seek new challenges".
The news of his departure has been met with regret by many of Spar's 2,600 retailers, with whom he has built a close rapport.
Peter Sichel, who owns two Spar stores in and around the Buckinghamshire village of Holmer Green, described him as "a genuinely great guy".
He said: "I'm saddened to hear of Jerry's departure as over the years my wife and I have grown very fond of him. He always took the time to speak to us at Spar events and has done a fabulous job of fighting for the sector and making the Spar brand shine. I doubt he will go to one of the multiples because he has always championed independents. Wherever he ends up, I wish him well."
Speaking exclusively to Convenience Store, Marwood said that spending time "on the shop floor" and with retailers had been the "most fun part of the job". He added: "I've had a brilliant time. This really is the best, most interesting, job in retail at the moment, and most of that comes down to the retailers. They are vibrant, entrepreneurial and incredibly inspiring people."
Retailers and the Spar board have credited Marwood with creating the strong business model and successful figures achieved by the Spar brand today.
"I'm not a believer in one big thing. For me, it's always been about delivering consistently high results and standards while also having fun along the way, and that is what I feel I have achieved," Marwood added.
The board has appointed a search company to find his successor, but retailers have warned that he or she will have "incredibly large shoes to fill".
Marwood will be involved in the recruitment and hand-over process, and he reassured retailers it would continue to be "business as usual" for now.
I'll be very sorry to see him go. He did a great job and he's done Spar a huge service. He's very approachable he's visited the store and I've met him at conferences and dinners and he's always friendly. He's got his finger on the pulse and always gets involved. He doesn't just react, he looks to the future. He's a driver and he's helped keep us ahead of the game." Malcolm Crump
Spar Compton, Wolverhampton
"Jerry has been a powerhouse of the trade, showing leadership and a passion for local retailing. Everyone who has worked with Jerry will have learned from his experience and judgment, and I was very fortunate to have benefited from his counsel and support when he was ACS chairman."
James Lowman Chief executive, Association of Convenience Stores