The British diplomat Tom Fletcher will be responsible for the UN's disaster relief organization, OCHA.
He replaces Martin Griffiths, who resigned in June due to health reasons.
It is the UN Secretary-General António Guterres who has appointed the Briton to the job.
This occurs at a time when there are major humanitarian crises in, among other places, the Gaza Strip and Sudan. At the same time, the UN is struggling to balance its budget.
Fletcher has previously been the UK's ambassador to Lebanon (2011-2015) and foreign and development policy advisor to three British prime ministers (2007-2011).
