Jeremy Hughes, chief executive of the Alzheimer’s Society, will step down within the next year, the charity has announced.
Hughes, who has led the charity since 2010, will remain as chief executive until his replacement can be found, the charity said in a statement.
A spokeswoman for the charity said it did not have details of what Hughes planned to do after his departure, but that he hoped "to continue to contribute to the dementia cause both nationally and internationally in the future".
Last week, a Twitter account purporting to be run by Alzheimer’s Society employees began publishing serious criticisms of the charity’s senior management.
A spokeswoman for the charity said it was "complete coincidence" that the Twitter account was set up a week before Hughes’s departure was announced, adding: "Jeremy’s decision to step down, as is usual for people at this level, has been planned for some time."
Hughes joined the charity from Breakthrough Breast Cancer, where he had been chief executive since 2005. He had previously led communications marketing at the International Federation of Red Cross and Red Crescent Societies and the British Red Cross.
In a statement, the Alzheimer’s Society credited Hughes with having led the charity’s "strong campaigning arm" and its successful Dementia Friends campaign.
He was awarded a CBE in 2015 for services to older people.
The same year he also won praise in the sector for his robust response to a critical article in The Sun newspaper that claimed 50p of every pound donated to the Alzheimer’s Society was spent on staff wages and pensions. He said The Sun had missed the point of the charity's work and called on sector leaders to help modernise how the media and the public understood the way charities worked.
In the statement announcing his departure, Hughes said he was "enormously proud" of what the charity had achieved during his time.
"Finding the right time to hand over the baton is always difficult, particularly when it involves such an inspiring team and organisation," he said.
"Leading the Alzheimer’s Society is without question the highlight and privilege of my professional life, and sharing this now allows time for a smooth handover to the next chief executive.
He paid tribute to his colleagues at the charity as "amazing people" and "guiding lights".
Stephen Hill, the charity’s chair, said Hughes had been "a remarkable leader".
Hill said: "His influence for the cause, both national and internationally, has been exceptional, and he has been a driving force in ensuring that the rights of people with dementia cannot be ignored. I’d like to thank him for his fantastic contributions and hope Alzheimer’s Society will benefit from his continued involvement in the dementia cause over the years to come."