UNESCO spokeswoman Joanna Sullivan says Preah Vihear was designated Monday at a meeting in Quebec City. "I can confirm to you that, yes, it was inscribed this afternoon," Sullivan said.
In 1962, the International Court of Justice in the Hague ruled Preah Vihear was located inside Cambodia's border, a decision opposed by many in Thailand.
Thai citizens were asked to donate money to help finance the country's push to defend the temple in the international court.
Cambodia has been trying to obtain the designation for the Khmer-style temple since 1992.
However, Thailand has vetoed its neighbour's previous submissions, fearing the status would include nearly five square kilometres of disputed land along the border.
In June, Thai Foreign Minister Noppadon Pattama signed a joint communique with Cambodia, endorsing the country's bid to nominate the temple as a world heritage site.
Tensions along the border boiled over last month when protesters threatened to evict Cambodians living in the disputed territory. Cambodia responded by closing access to the temple.
The temple's select status as a world heritage site will attract tourists and grants from the United Nations' World Heritage Fund.