Stephen Hale, chief executive of Refugee Action, is to step down after six years in the role.
He said he would leave in two months’ time to take on a new role at a “new global organisation focused on climate change”, but did not reveal the identity of the organisation.
Tim Naor Hilton, head of asylum at Refugee Action, will act as interim chief executive until a permanent successor is found.
He said: “It has been an absolute joy and privilege to lead Refugee Action, and to work closely with so many brilliant people across the sector and beyond.
“Six years have flown by, and I am sure the next two months will too.
“The climate community has many heroes, many incredible organisations, and many victories. I look forward to re-engaging with the definitive challenge of our lifetimes.”
Penny Lawrence, chair of Refugee Action, said the charity had grown in reach and influence with humility and generosity under Hale’s leadership.
“Stephen is one of those rare multi-talented chief executives, equally capable in relationships and strategy.
“Though he will be sorely missed, Stephen leads a fabulously talented team and we're proud his skills and talents will be used in the fight to tackle climate change,” she said.