Rick Holland, part-time chief executive of the Charity Employees Benevolent Fund, has left the organisation six months after he was appointed.
The news comes three weeks after the formal launch of the charity, which was founded in 2004 and is now attempting to expand.
A spokeswoman for the charity said Holland, former head of fundraising at the MS Society, had left by mutual agreement. However, Holland told Third Sector this was "inaccurate".
The spokeswoman said his departure was amicable but the decision was taken because Holland had not raised sufficient funds.
In a statement, Holland said: "I'm surprised and disappointed by the CEBF's action, less than two weeks after our fantastic launch on 12 November.
"It's a really a great shame that the CEBF risks losing the goodwill that we worked so hard to create."
The fund, set up to help charity workers in financial difficulty, will recruit a replacement.
"Whoever we recruit has to have to the right contacts and networks to keep the charity going," the spokeswoman said.