Dennett said it had been a "privilege" to serve the co-operative, but was looking ahead to a new chapter in his career.
Travel and post office operations manager Dennett will be succeeded by interim head of retail Shaun Davies.
Davies, who himself has more than 30 years' retail experience, will take operational responsibility for travel and post office.
Dennett will leave his post at the end of January.
“It has been a privilege to spend three decades with this business, growing alongside the teams and customers who make it such a special place to work," he said.
"I am excited for the next chapter in my career, but I will always be grateful for the friendships, opportunities, and experiences I’ve gained here.”
Steve Leach, Lincolnshire Co-op's chief operating officer, added: “Wayne has played a pivotal role in shaping our travel and post office operations.
"His dedication to our colleagues and customers has made a lasting impact. While we are sad to see him go, we are grateful for his outstanding service over the past 32 years and wish him every success in his new role.”
Lincolnshire Co-op has 13 travel branches. Earlier this year, its Louth branch reopened after a £160,000 makeover, one the group said would serve as a blueprint for a full revamp of its network.
