Results announced on Tuesday, showed the 72-year-old defeated President Goodluck Jonathan in a win described by the UN as “testament to the maturity of Nigeria’s democracy”.
Speaking in the capital Abuja yesterday, Buhari said his government would “spare no effort” to defeat the armed group.
“Boko Haram will soon know the strength of our collective will and commitment to rid this nation of terror and bring back peace,” Buhari said in his first formal speech since winning the election.
“We should spare no effort. In tackling the insurgency, we have a tough and urgent job to do.”
Buhari also said that his administration would not tolerate corruption, an issue outgoing Jonathan was widely criticised for.
The president-elect described Jonathan as “a great Nigerian” and said the outgoing president “has nothing to fear from me”.
Buhari added: “Democracy and the rule of law will be established in the land.
“Let’s put the past behind us, especially the recent past. We must forget our old battles and past grievances and forge ahead.”
The margin of victory — Buhari received 15,4 million votes to Jonathan’s 13,3 million — was enough to prevent any legal challenge.
In an unprecedented step, Jonathan called Buhari on Tuesday to concede defeat and issued a statement urging his supporters to accept the result, a signal of deepening democracy in Africa’s most populous nation that few had expected. Jonathan is set to officially handover the seat on May 29.
“Nobody’s ambition is worth the blood of any Nigerian,” he said in a statement issued after his election defeat.
Jonathan’s People’s Democratic Party (PDP) has been in charge since the end of army rule in 1999 but had been losing support due to several oil-sector corruption scandals and killings by rebel group Boko Haram in the northeast.
Former military ruler Buhari became the first Nigerian to defeat a sitting president through the ballot box.
Victory for Buhari marks the first time in Nigeria’s history that an opposition party has democratically taken control of the country from the ruling party.
Al Jazeera’s Haru Mutasa, reporting from Lagos, said there was shock that Jonathan had congratulated Buhari and that violence had not followed the announcement.
In the 2011 election, more than 800 people were killed in protests after Buhari was defeated by Jonathan.
“The announcement has been greeted with celebrations across the country,” Mutasa said.
“Many people are excited and hope this will mark a new beginning and move the country forward.”
Hundreds of Buhari’s supporters gathered to celebrate outside his home in Abuja, with some brandishing brooms to symbolise his promise to clean up corruption.
His supporters told Al Jazeera that the vote was “free, fair and without irregularities” as the country ushered in a new era. — Al Jazeera.