Nuysi triumphed with 73 percent of the vote while his ruling left-wing Frelimo was also victorious in the legislative and provincial races.
The electoral body said Ossufo Momade, candidate for former guerrilla movement turned the main opposition right-wing and nationalist party Renamo, which has already rejected the results, trailed behind with 21.8 percent of the vote.
Nuysi who will remain in power for a second five-year term will bear the responsibility for overseeing a gas boom led by oil giants such as Exxon Mobil Corp and Total; battling an Islamist insurgency, and delivering on a peace deal signed two months ago with Renamo.
“I will work so that we can have a prosperous, equitable and fair Mozambique,” Nuysi told supporters in a suburb of the capital Maputo. “In these elections, the Mozambican people won,” he added vowing to further develop the country and hurry the enforcement of the peace deal with the opposition.
However, the deal is at risk of collapsing over the rejection of the results by the Renamo party, who accused the government of using violence and intimidation. Frelimo for its part says the elections were free and fair.
It was hoped the Oct. 15 poll could set the seal on the fragile peace pact, designed to put a definitive end to four decades of violence between Frelimo and Renamo. The two fought a 16-year civil war that ended in a truce in 1992 but have clashed sporadically since.
According to analysts, a return to a full-scale conflict is highly unlikely even if the deal breaks down, but low-level violence, including from an armed group of breakaway former Renamo fighters, could worsen.
Turnout was a little bit higher than in the previous general election in 2014, with just over 50% of the more than 13 million registered voters coming out to cast their ballots.