Muhammadu Buhari will be Nigeria’s new president, winning the election by 2.1mn votes over incumbent Goodluck Jonathan, according to Reuters.
President Jonathan is reported to have called and congratulated Mr Buhari for his election victory.
Nigeria's opposition All Progressives Congress (APC) declared the victory for former military ruler Mr Buhari and said hailed the historic democratic transfer of power.
"The people of Nigeria have taken over," an ecstatic APC spokesman Lai Mohammed told Reuters.
"This is the first time in Nigeria that a sitting government will be voted out of power using purely democratic means."
The United States said it is ready to work with anyone democratically elected as president.
"I would reiterate that the U.S. is ready to work with whichever candidate the Nigerian people elect through the democratic process," said the U.S. State Department official, who spoke on condition of anonymity to Reuters.
"Buhari has peacefully contested the last few presidential elections and accepted the results of those votes, even when he questioned the credibility of the process," he said.
Buhari records early victories, concern about political interference (30 March 2015)