The former newspaper journalist has also held senior roles at Edelman and MHP.
Cleland be responsible for leading the Hanover corporate practice on a day-to-day basis, broadening the group’s fast-growing technology and financial communications capabilities.
He reports into managing director of corporate and brand Gavin Megaw.
"I'm already hugely impressed by the clarity of thought, the creativity and the energy at every level at Hanover," Cleland said.
"We have all the tools we need to continue to expand in London and beyond, and I'm glad to be on board for what's going to be an exciting, fun time for the team."
Megaw said Hanover were looking for the "hottest strategic communications talent" to fill the role.
"Gary was the outstanding candidate in that process. His strategic approach, campaign mind-set and cultural fit meant he was a direct match to our aspirations," he said.
"His appointment to this newly-created role comes at a crucial time for Hanover as we continue to invest to realise our ambition of becoming the best in class corporate reputation agency around."
This year Hanover has made several senior appointments, including Andrew Baiden as MD of its offshoot The Playbook.