Mark Goldring, chief executive of Oxfam, is to stand down at the end of the year.
Goldring, who joined Oxfam in April 2013, said it was "with a very heavy heart" that he had decided to leave the role, but "the time is coming for a new leader".
He said in a statement to the charity’s supporters that the past few months had been tremendously difficult for all involved with Oxfam.
"Along with all of you, I feel anger at the impact of the abhorrent abuse of power by those individuals in Haiti in 2011 and Oxfam's failure to protect the women we were there to support," he said.
"I also feel sadness at the impact of the recent sector-wider coverage, which undermines public support for development and humanitarian action in a way that will harm people living in poverty across the world.
"We need to ensure that Oxfam and all agencies are safe and worthy of public confidence, and we need to win trust back."
Goldring, who before joining Oxfam was chief executive at the learning disability charity Mencap, said Oxfam had achieved much in recent years. "I am proud to have played a part in that, but I think the time is coming for a new leader," he said.
He said the process of renewal for the charity would be a long-term one.
"As well as learning lessons, Oxfam GB needs to win back public trust, rebuild relationships and regain our own voice," he said.
"And we need to use the challenges and shocks to rethink exactly what kind of organisation we want to be in the next decade.
"Leading this journey feels to me like the role for a new chief executive, working with volunteers, staff, partners, trustees and as part of an Oxfam International process over an extended period."
Caroline Thomson, chair of Oxfam, said "it was with great sadness and with thanks for his dedication and leadership" that she had accepted Goldring’s decision to stand down.
She said Goldring had faced "the test of a lifetime managing the crisis that hit us in February and related to events before he joined".
She said: "He rose to the immense challenge and his leadership has been invaluable through it. It is testament to his integrity and humility that Mark will see through the next few difficult months.
"Mark's decision today is in keeping with his work over the past five years. His top priority has always been to ensure that Oxfam has a great future, focused on the people we are here to serve, helping them to escape the dirty water, hunger and other daily realities of life in poverty now and for good."
The charity said Goldring would continue in the role until a successor had been recruited and was in post.