Israel has formally notified the UN's culture and education body of its withdrawal from the organization, two months after it announced it would follow the United States by walking out over resolutions critical of the Jewish state.
In a statement Unesco chief Audrey Azoulay said she had been officially notified on Friday that Israel would leave on December 31, 2018.
"I regret this deeply, as it is my conviction that it is inside Unesco and not outside it that states can best seek to overcome differences in the organization´s fields of competence," she said.
The October 12 announcement by the United States that it was pulling out of the organization underlined Washington's drift away from multilateral institutions under nationalist President Donald Trump.
The US at the time accused Unesco of having an "anti-Israel bias" – a sentiment echoed by Israeli Prime Minister Benjamin Netanyahu who accused Unesco of becoming "the theatre of the absurd."
Their pullout followed two Arab-sponsored resolutions adopted by Paris-based Unesco this year which were critical of Israel.
One referred to the Jewish state as "the occupying power" in the divided city of Jerusalem. Another declared the Old City of Hebron in the occupied West Bank a Palestinian World Heritage site.
Tensions had been bubbling since Unesco controversially admitted Palestine as a member state in 2011 – a move opposed by the US and Israel, who argue that any recognition of Palestinian statehood must await a negotiated Middle East peace deal.
The US cut funding to Unesco over the decision, depriving it of around a fifth of its budget.
The 195-member body is best known for producing a list of World Heritage sites that have become tourist favourites.
Israel, which has been a member since 1949, has nine sites on the list, including the ancient Masada fortress next to the Dead Sea.
Unesco also runs science, educational and cultural programmes, including programmes to educate people about the Holocaust and promote intercultural dialogue.