Mandy Johnson, chief executive of the Small Charities Coalition, has resigned after just over a year in the role.
A statement from the SCC said today: "We are sorry to announce that Mandy Johnson has resigned from her post as chief executive of the Small Charities Coalition.
"We thank Mandy for doing such a terrific job in raising the profile of the SCC over the past year and we wish her all the very best for the future."
The statement said the charity would be appointing an interim chief executive as soon as possible.
Rachel Harding, head of services, and Lizzie Walmsley, head of communications and external affairs, will manage its office with the support of the board, the charity said.
"We have an excellent team in place, so it’s business as usual," the statement said.
Over the summer, Johnson took part in a Third Sector article and photoshoot celebrating the number of women leading charity sector representative bodies. However, she subsequently issued a statement on Twitter on behalf of the SCC expressing her regret about taking part in the article after some in the sector criticised the piece for its lack of diversity. Johnson also asked for her contribution and photo to be removed from the feature.
Third Sector understands that Johnson's actions led to tensions between her and SCC's board.
Johnson is credited with raising the profile of the SCC and small charities during her time in charge.
Earlier this year, she also won plaudits for setting up a list of non-male charity sector conference speakers in a bid to improve diversity in event line-ups. The list also highlighted potential speakers who do not identify as white in order to improve the racial diversity of speakers at sector conferences.
Johnson, who does not have another role lined up, said it had been a privilege to have led the SCC.
"I saw first hand how dedicated volunteers and staff working for small charities are making positive differences to communities across the UK," she said.
"I also saw some of the challenges and difficulties facing small charities as they work to thrive in a society that so often sees big as better.
"I will continue to champion the work of charities of all shapes and sizes and encourage others to do the same."