A three-member team selected by the world body has six months to investigate "the facts and circumstances" surrounding Bhutto's death and report back to the U.N. Secretary General, the BBC reports.
The investigation is headed by Heraldo Munoz, Chile's ambassador to the United Nations.
Other team members are Marzuki Darusman, the former Indonesian attorney general, and Peter Fitzgerald, who headed the inquiry into the assassination of former Lebanese Prime Minister Rafik Hariri.
The three will travel to Pakistan later this month.
Bhutto was shot to death in 2007 as she left a rally of supporters in Rawalpindi.
Pakistan's Interior minister told the BBC his government thinks the U.N. investigation is necessary.
"We want to know who was behind this, who had conspired it, who has financed it. And we think this was a big international conspiracy," Interior Minister Rehman Malik said.