The International Atomic Energy Agency (IAEA) on Monday formally appointed Yukiya Amano of Japan as its new director general from December 1, succeeding Mohamed ElBaradei.
The 150 member states of the UN nuclear watchdog approved Amano -- who has been Tokyo's ambassador to the IAEA -- by acclamation on the first day of the agency's annual weeklong general conference
ElBaradei is stepping down at the end of November after 12 years in office.
Amano, 62, was chosen by the IAEA's 35-member board of governors -- its main decision-making body -- in July, but his appointment had to be formally adopted by all 150 member states at the general conference.
He will take up the position on December 1 and initially serve for a period of four years until end-November 2013.
After being sworn in, Amano described his appointment as "truly a great honour."
"I humbly accept the appointment to this prominent post and express my sincere gratitude to the member states for their support and trust," he told the assembly.
"I would also like to take this opportunity to express my profound respect to Dr Mohamed ElBaradei for his outstanding contribution to the agency during his 12-year tenure.
"His tireless efforts and selfless dedication towards world peace and prosperity through the activities of the IAEA will undoubtedly be remembered."
ElBaradei, 67, has frequently come under fire, particularly from the United States, for being too soft on Iran, which is suspected of seeking to develop the atomic bomb under the guise of a civilian nuclear energy programme.
In his own opening address to the conference, ElBaradei wished Amano "every success" in his new position.
"I ... offer him my full support. I trust that he will lead the agency with vision, impartiality and courage," ElBaradei said.