The 76-year-old who had predicted his win defeated his main rival and former Vice President Atiku Abubakar, with a margin of nearly four million votes of the total vote cast.
The election has suffered a one week postponement from it’s earlier scheduled date of February 16.
Following the release of the results, Mr Abubakar’s People’s Democratic Party (PDP) has rejected the result. Turnout was a record low at 35.6%.
Violence marred the run-up to Saturday’s poll but so far, no independent observer has cited electoral fraud in the February 23rd polls.
“The new Buhari administration is tasked with intensifying its efforts in security, restructuring the economy and fighting corruption,” Mr Buhari said after his victory was officially announced.
Buhari had predicted his win during a brief interview while casting his vote alongside his wife..