Gambari, a former Minister of Foreign Affairs, replaces Mallam Abba Kyari, who died last month of COVID-19.
The new Chief of Staff will resume work at the Presidential Villa on Wednesday.
Gambari, as foreign minister, played a key role in quelling the diplomatic uproar generated by the failed attempt to kidnap Mallam Umaru Dikko from UK by the Buhari military government.
A scholar and seasoned diplomat, Gambari served as minister of External Affairs between 1984 and 1985. He was appointed by former United Nations Secretary Ban Ki-moon and the chairperson of the African Union Commission as Joint African Union-United Nations Special Representative for Darfur in 2010.
He also served as Special Adviser on the International Compact with Iraq and Other Issues for the UN Secretary General. Prior to that, he served as Under-Secretary General of the United Nation for the Department of Political Affairs (DPA).
The new chief of Staff, an Ilorin prince, was born on November 24, 1944