Graham Turner, chief executive officer of North Somerset Council, is to retire in November after over 24 years' service with the council.
He has given six months' notice to give the council the opportunity of finding a successor before he leaves.
He has been chief executive officer for more than 12 years.
He said: "This has been a very difficult decision for me as I love North Somerset and feel that I have been incredibly privileged to have had this role.
"I have had the good fortune to work alongside such dedicated and committed people, both within the council and within our partner organisations."
Councillor Nigel Ashton, Leader of North Somerset Council, said: "Graham has made a huge contribution to North Somerset during his 24 years at the council, the last 12 in the top job.
"He is respected not only in North Somerset but across local government. It will be a challenge to replace him. He has led the council into closer and more fruitful relationships with other organisations like the police, health service and the college, and the innovative partnerships we now have will stand as testament to Graham's progressive approach. On a personal note, it has been a privilege to work with him. I think it will be some time before people really understand his contribution and the loyalty he has engendered in his team."
The recruitment process will be agreed at a meeting of the council, with a view to an appointment in July.
Mr Turner joined the former Woodspring District Council in 1989, having previously worked in Norfolk, Warwickshire, Humberside and Nottinghamshire. He was appointed as North Somerset's chief executive officer in 2001.
