UNITED NATIONS - With a pledge to make United Nations effective, former Portuguese Prime Minister Antonio Guterres took oath of office as the next Secretary-General of the United Nations, becoming the ninth UN chief in the body’s 71-year history.

Guterres, 67, was sworn in by the president of the General Assembly, Peter Thompson, at a solemn ceremony, as a loud applause rang out.

The former UN refugee chief was elected to the top job by acclamation in the 193-mmber Assembly in October. He will take over duties from Ban Ki-moon on Jan. 1.

Speaking after talking the oath of office,  Guterres pledged to reposition development at the centre of the Organization’s work and ensure that the UN can change to effectively meet the myriad challenges facing the international community.  “The United Nations needs to be nimble, efficient and effective. It must focus more on delivery and less on process; more on people and less on bureaucracy,” Guterres said after taking the oath of office at a ceremony before the 193-member UN General Assembly.

Guterres, a former Prime Minister of Portugal (1995 to 2002) and former UN High Commissioner for Refugees (2005-2015) replaces Ban Ki-moon, who steps down at the end of the month after leading the global Organization for the past 10 years.

“The United Nations was born from war. Today we must be here for peace,” he added, noting that addressing root causes, cutting across all three pillars of the UN: peace and security, sustainable development and human rights, must be a priority for the Organization.

He was formally appointed by the General Assembly on 13 October in what was the culmination of an historic process Member States set in motion late last year: the selection of a new UN Secretary-General, traditionally decided behind closed-doors by a few powerful countries, for the first time in history, involved public discussions with each candidate vying for the leadership position.  In his brief speech, Guterres said the world body must work to simplify, decentralize and make more flexible its sprawling bureaucracy.

“It benefits no one if takes nine months to deploy a staff member to the field,” he said.

The swearing-in came after the 193 General Assembly members paid tribute to Ban, ending with a standing ovation for the outgoing UN chief. The swearing-in ceremony included the UN’s top leaders and was attended by dignitaries.

US Ambassador to the UN Samantha Power lauded Ban’s accomplishments while in office and said she was confident Guterres is the right person to replace him. “He is the man for the job in such challenging times,” she said.

The selection of a new secretary-general had traditionally been decided behind closed doors by a few powerful countries. But this year, the process involved public discussions with each candidate who was campaigning for the job. UN chiefs are charged with promoting sustainable development, working for peace around the globe, protecting human rights and dealing with humanitarian catastrophes.

Ban served two five-year terms.