Once stepped down from the group, Hewitt will take up the role of chairman of the English Football Association in January 2022.
The board has commenced a formal process to recruit her successor which is led by Graham Clemett, senior independent director.
Hewitt said: “TRG is a fantastic business, full of outstanding people, who care passionately about our customers and the food and service they deliver.
“I remain fully committed to working with Andy and Graham for the rest of the year to ensure the recruitment of a strong successor and a smooth transition.”
Andy Hornby, CEO, The Restaurant Group, added: “On behalf of the board and everyone at TRG, I would like to thank Debbie for the significant contribution that she has made to the business. She is a proactive chairman who has built and led a high-quality Board and proactively engaged with all stakeholders throughout her tenure.
“The FA have chosen Debbie for her extensive chair expertise across a wide range of business sectors, and there is no doubt that TRG has benefitted from that experience. We wish her every success in this new role.”