António Guterres | Salvatore di Nolfi/EPA Portugal’s António Guterres to be new UN chief He held off a late challenge from European Commission Vice President Kristalina Georgieva.

António Guterres, a Socialist former prime minister of Portugal, is the unanimous choice of the 15-member United Nations Security Council to become the next leader of the organization, the ambassadors announced on Wednesday.

Guterres will replace Ban Ki-moon as a secretary-general in January. He's a U.N. insider, who until last December had led the U.N. refugee agency.

The 15 ambassadors of the U.N. Security Council appeared in the lobby of United Nations headquarters in New York to make the announcemnt.

With the support of all of the members of the U.N. Security Council, the decision is all but sealed, and will be confirmed in a formal vote on Thursday 10 a.m. New York time.

After a long campaign involving 13 candidates, Guterres, who from the start led the race, held off a late challenge from European Commission Vice President Kristalina Georgieva.

In choosing Guterres, the U.N. has set aside an informal tradition of rotating the presidency by region. Had the tradition been observed, this term would have been for a candidate from Eastern Europe.

Eastern Europe is the only region that has never held the top U.N. position. The Security Council also ignored pressure to select a woman to hold the top post.

Benjamin Oreskes contributed to this article.