Tony Charalambides, managing director of the telephone fundraising agency Listen, has announced he will leave the company at the end of the month.
In a statement, Charalambides said he was moving on to pursue an "exciting new project in the field of fundraising", but a spokesman for Listen declined to give any further details.
Charalambides has held the post at Listen since founding it in 2008 and has led the company through a difficult couple of years after it was the focus of a Mail on Sunday piece in 2015, accusing it of using high-pressure tactics.
The company made a loss of £202,895 in the year to March 2016, from a profit of £954,538 in the previous year, amid what it described in its 2015/16 accounts as a "permanent" reduction in the size of the telephone fundraising market.
In the same year the company reduced its staff from 332 to 286 but unlike a number of its contemporaries, including another of Charalambides’s firms, the face-to-face agency Tag Campaigns, which went into administration in January 2013, seven months after a Sunday Telegraph article alleged it was breaking fundraising rules, Listen did not close down.
In a statement about his departure, Charalambides said: "I have had a stimulating and highly enjoyable nine years at Listen, and been lucky to work with a hugely talented team in delivering many successful fundraising campaigns for our clients.
"I feel it’s now time to move on and focus on other interests – in particular to work on an exciting new project in the field of fundraising.
"I will always retain a keen interest in Listen’s future activities and the enormously valuable work of its many clients."
He will also retain his shareholding in the company.
Charalambides has also been involved in the sector through his involvement in a task group set up by the Institute of Fundraising and is listed as a contributor to the Commission on the Donor Experience.
A spokesman for Listen’s parent company TCLLH, said: "Understandably, Tony feels the time is right for a fresh challenge. He will be sorely missed.
"However, he leaves behind a team of vastly experienced and talented senior managers who we are confident can take the company forward.
"We wish Tony all the best for the future and would like to thank him for all his hard work over the years. He has been a fully committed MD who has worked tirelessly to build and then maintain Listen’s award-winning reputation."
In a statement, Listen said its senior leadership team would be restructured with new director roles being created. These will be appointed imminently, the statement said.