That moment also ended the reign of Goodluck Jonathan as leader of the most populous black nation on earth.
Vice President Yemi Osinbajo was the first to be sworn in in a ceremony conducted by the Chief Justice of Nigeria, assisted by the Chief Registrar of the Supreme Court.
Shortly after Mr. Buhari was sworn in, the outgoing president congratulated him and presented to him copies of the Nigerian Constitution, and the National and Armed Forces Flag.
Messrs Buhari and Osinbajo of the All Progressives Congress were elected at the March 28 presidential election.
This is the first democratic transfer of power from one political party to another in Nigeria’s history.
The inauguration ceremony is still underway.