Ban's spokeswoman, Michele Montas, said Ripert would assist the Pakistan Government and the international community to respond to the current humanitarian crisis in the country.
"Ripert is to assist the government of Pakistan and the international community in responding to the present humanitarian recovery and reconstruction needs related to the country's displacement crisis," The Dawn quoted Montas, as saying.
Ripert, who will step down as UN ambassador at the end of this month, would be on the post for an initial period of six months.
Ripert, 56, has addressed humanitarian issues concerning several countries such as Myanmar, Darfur and Sri Lanka in the Security Council in the past.
According to an estimate more than 1.9 million people have been displaced in Pakistan following the military's massive offensive against the Taliban and other extremist groups since mid April.
However, the UN has said that about two-third of the internally displaced people (IDP) have returned home.