Unicef UK has appointed Nick Roseveare as interim executive director after the resignation of Mike Penrose.
Penrose announced in August that he would step down in the autumn to "pursue a number of personal projects" after three-and-a-half years in the post.
He will take up the role at Unicef on Wednesday and remain in post "until a permanent executive director is confirmed", a statement from the charity said.
Roseveare said he was "keen to maintain and help to accelerate progress on key projects and processes for next year, and support all colleagues to feel empowered to bring their best energies and expertise to their roles".
Douglas Alexander, chair of Unicef UK, said: "Nick brings a wealth of experience and expertise to the role, and the board and I have every confidence he will provide capable and effective leadership to Unicef UK over the coming months."