John Ging, the director of the UN Relief and Works Agency (UNRWA) in Gaza to take up a senior position in the UN in New York.
The 45-year-old Irish native has worked in Gaza since 2006 and is recognized as a leading advocate for the rights of the Gaza population and has openly criticized Israeli government policy.
In Gaza he has been the target of several assassination attempts, as well as death threats, while Islamist opponents have openly attacked projects he has promoted.
The UN employee had described the blockade of Gaza as a “medieval siege” and has said that Israel's policies were responsible for breeding a new generation of militants.
His departure from the UN in Gaza will be welcomed by many in the Israeli political and military establishment.
Barbara Shenstone, the director of UNRWA operations in the West Bank has also announced she was leaving to return to her home country, Canada.
Speaking about the departures, the agency said: "Barbara and John have made exceptional contributions to UNRWA's work under the most difficult circumstances."
Filippo Grandi, the commissioner-general said: "Their commitment to ensuring the quality of UNRWA services has been extraordinary; their advocacy in support of rights has been outstanding – be it amidst heavy bombardment in Gaza during armed conflict or in responding to the abysmal rights abuses in the occupied West Bank."
Ging will take up a role with the UN’s Office for Coordination of Humanitarian Affairs in New York.
A UNRWA spokesman described the role as “a big promotion”.
UNRWA provides services for 4.7million refugees in the Palestinian territories.