Sir Alan Parker has resigned as Save the Children's international chairman after 10 years in the role, the organisation has said.
He also stepped down from the boards of the Save the Children Association and Save the Children International.
Sir Alan was due to leave in December but "felt it right at this moment to bring forward his succession".
In a letter to colleagues, he said a change was needed given the challenges facing the charity and the sector.
In February, the BBC revealed Save the Children's ex-chief executive Justin Forsyth faced three complaints of inappropriate behaviour towards female staff before he left the charity in 2015.
Days later, Mr Forsyth resigned from his role as deputy director of UNICEF, saying he did not want coverage of his past to "damage" the charities.
Mr Forsyth said that he had taken "responsibility" for his mistakes "many years ago", but strongly denied a number of claims.
Evidence later emerged - in leaked documents seen by the BBC - that suggested the Save the Children had "failed" to adequately deal with the allegations.
The report from 2015 also suggested then chairman Sir Alan's "very close" relationship with Mr Forsyth may have affected how he responded to complaints.
In his resignation letter, Sir Alan said Mr Forsyth's case had been handled by HR and senior trustees, and was now being reviewed by the Charity Commission.
"This is an important review and I will work with them to assist in any way I can," he wrote.
He went on to say this was "an extraordinary time" for the sector, with more displaced children than "at any time in history".
"There is an urgent and pressing need to rebuild trust and confidence," he said.
"If we do not, some of the world's poorest and most vulnerable children will suffer."
Helle Thorning-Schmidt, CEO of Save the Children International, thanked Sir Alan for "the time and dedication he has invested in our important cause".
Sir Alan is the founder and chairman of the PR firm Brunswick and counts former prime ministers among his friends.
Gordon Brown is godfather to his youngest son, and when David Cameron left Number 10, it was Sir Alan's west London mansion that became the Camerons' temporary home.