Unicef executive Justin Forsyth has resigned after allegations were made of inappropriate behaviour while he worked for Save the Children.
The announcement comes after his former colleagues complained about his conduct.
Mr Forsyth previously admitted making "some personal mistakes" during his time at Save the Children.
He said he is stepping down "because of the danger of damaging both Unicef and Save the Children" and not because of his past mistakes.
"I want to make clear I am not resigning from Unicef because of the mistakes I made at Save the Children.
"They were dealt with through a proper process many years ago. I apologised unreservedly at the time and face to face. I apologise again."
Recently Forsyth admitted he faced complaints about "inappropriate" behaviour during his time in charge at Save the Children.
He acknowledged he caused "hurt and offence" to three female colleagues during his tenure between 2010 and 2015.
Save the Children said separate investigations were carried out into each complaint which resulted in apologies from Mr Forsyth.
The charity has since apologised to the female employees, admitting their claims were not properly dealt with at the time.
In a statement on Thursday he said: "There is no doubt in my mind that some of the coverage around me is not just to (rightly) hold me to account, but also to attempt to do serious damage to our cause and the case for aid.
"I am resigning because of the danger of damaging both Unicef and Save the Children and our wider cause.
"Two organisations I truly love and cherish. I can't let this happen."
The disclosures came after Brendan Cox, the widower of murdered MP Jo Cox, admitted that he made "mistakes" and behaved in a way that caused some women "hurt and offence" when he was working at Save the Children.
Mr Cox and Mr Forsyth had previously worked together at 10 Downing Street under Gordon Brown