Marks, who led a deal in June to buy over 600 bank branches from Lloyds Banking Group, said it was “time to hang up my boots” after 45 years with the firm.
It is understood the Co-op has appointed executive search firm Sam Allen Associates to headhunt potential candidates to replace him. Both external and internal candidates are being considered.
The Co-operative Group, long seen as a staple of the supermarket sector, moved to acquire 632 Lloyds branches to boost its high street banking capability.
Marks said he had wanted to step down in the middle of last year but decided against it to focus on getting an agreement with Lloyds.
He added his priority over the next nine months would be getting the Lloyds deal “signed, sealed and delivered”.
His successor will need to focus on the consolidation of the Co-op’s rag tag collection of businesses, which include retail, banking, travel and funeral services.
“The business has gone through massive change and grown enormously – it’s time now to really integrate those businesses,” Marks said.
“Strategically, we need to build scale to compete.”
Asked about who should replace him, Marks – who will step down at the firm’s next annual meeting – said: “This is a decision for the board and I want to respect their authority. They will make the decision but what it needs is someone who is a strategic business person.”
He added: “I have always planned to target 63 as the time to hang up my boots and I’m 63 this October. I’ve got mixed feelings about it, but I’m ready for it.
“It’s been quite tough over the last six years and it takes a lot out of you – I’m ready for a rest.”
Marks said he would not divorce himself from the business world completely, and was considering non-executive roles or chairmanship of a business in future on a part-time basis.