Mike Penrose is to step down as executive director of Unicef UK, the charity has announced.
A statement from the charity today said Penrose, who has been in the post since April 2016, would leave in the autumn "to pursue a number of personal projects".
The statement said the charity was grateful to him for his "significant contribution and unwavering commitment to championing children’s rights, both in the UK and around the world".
Penrose joined Unicef after two and a half years as chief executive of the French humanitarian charity Action Contre La Faim.
In 1996 and on his first mission at his first stint at Action Contre La Faim, he and several colleagues were kidnapped by Chechen rebels and held hostage for two months.
In the statement today, Douglas Alexander, chair of Unicef UK, said: "Mike has had a distinguished career in humanitarian work and during his time at Unicef has been a fierce and effective advocate of children’s rights.
"We wish him well for the future."
Penrose said it had been a "tremendous honour" to serve as executive director of the charity.
"Unicef UK is a dynamic and inspiring organisation and the commitment of all its employees to champion children’s rights never ceases to amaze me," he said.
"I feel very proud of the work that has been achieved for children both here in the UK and around the world."
The charity said it would begin the process of appointing a new executive director immediately.
Unicef UK’s latest set of accounts, filed with Companies House last month, showed its income fell slightly in 2018 to dip below £100m for the first time since 2014.
Income from donations and legacies fell from £92.4m to £89.5m, mainly due to downturns in revenue from direct marketing and trusts and foundations.