Beaumont, 57, has been at the helm of the UK's largest co-operative society for the past five years. He said that, after a sustained period of restructuring and modernisation of the £8bn turnover group - which spans food stores, funerals, pharmacies and financial services - he would be leaving a business that was in good shape for the future.
Last month the society announced a 32% increase in first half profits to £157.4m.
Beaumont said: "I believe we now have a strong platform for the next phase of the Co-operative Group's development. While we have had to take some difficult decisions to get to where we are today, it has been a privilege and immensely rewarding to have led the group through a profound period of change. I look forward to building on our progress over the next 12 months before handing over the baton."
Beaumont said that during his stewardship the Co-operative Group has realigned its portfolio, focusing on customer-facing businesses.
It had also restructured, bringing its insurance and banking businesses together, and had added new businesses to its portfolio.
Chairman Bob Burlton said: "Martin has successfully steered the group through a defining period in its history. We have tackled the legacy and structural issues which have impeded our performance in the past. We now have effective business strategies in place across the group.
"The launch of our new brand and membership proposition will increase our appeal to the growing number of consumers who share our values. On behalf of the board I'd like to thank Martin and wish him a happy retirement."
The board will discuss appointing a successor when it meets in November.