The 69-year-old, who had previously been the FTSE 100 firm’s’ deputy chairman, said he was leaving with Barclays in “very good shape”, but that it is an “appropriate moment for a change”.
“Going forward, I will be concentrating on my public sector activities in the UK, my work with Deloitte in Europe and globally, my work in the Gulf, India, China and elsewhere in Asia-Pacific,” Grimstone added.
“There will doubtless be many other exciting public and private opportunities to pursue.”
Barclays chief executive Jes Staley said it had been a “privilege” to work with Grimstone.
“I am deeply grateful to him for the support and counsel he has provided me personally, as well as for his immense contribution to the turnaround of our Corporate & Investment Bank in particular.”
Nigel Higgins, the incoming chairman-elect of Barclays, will also assume the chair of Barclays Banks when he joins at the beginning of March.
Barclays shares were down 2% to 157.7p on Friday morning.