Martin Sime, chief executive of the Scottish Council for Voluntary Organisations, is to retire after more than 25 years in the role.
Sime, who joined the umbrella body in 1991, said today he would stand down at the end of the year.
Neville Mackay, interim convenor of the SCVO, said Sime had "transformed the landscape" in which the voluntary sector in Scotland operated.
"Among his many achievements are driving positive change in charity law, charity finance and the esteem with which the sector is held by the public and parliament," said Mackay. "We are grateful for his many accomplishments over more than 25 years and wish him a long and happy retirement."
Sime, a former Third Sector columnist, has been a forthright commentator at times. In 2015 he called for William Shawcross, chair of the Charity Commission, to resign with immediate effect because of comments Shawcross had made about charities including Oxfam and the RSPCA in an interview with The Times newspaper.
Sime said in a statement today: "It has been my privilege to hold such a fantastic position for over a quarter of a century and to have been part of the changing face of the third sector throughout that time.
"I have met and worked with some truly inspiring people and wonderful causes."