Pierre Claver Ndayicariye, head of the electoral commission, told reporters on Friday that Nkurunziza had garnered 69.41 percent of the votes cast in the polls that took place on Tuesday.
Nkrunziza's nearest rival, Agathon Rwasa, took 18.99 percent.
The opposition says Nkurunziza's bid violated the constitution.
The vote took place on Tuesday, despite calls by African leaders and Western powers for it to be delayed due to the tensions in the country.
A day after the election, however, country's leading opposition politician called on President Nkurunziza to hold talks with rivals and form a national unity government, saying it could help avert a new civil war.Nkurunziza's decision to seek a third term had plunged the small east African nation into its biggest crisis since an ethnically charged civil war ended in 2005. The opposition says Nkurunziza's bid violated the constitution.
Amnesty International in a report said that the police used excessive lethal force against protesters opposed to Nkurunziza's bid for a third term.
The rights-advocacy group, which released on Thursday its report Braving Bullets - Excessive force in Policing Demonstrations in Burundi, said that authorities "repressed demonstrations as if they were an insurrection".
Dozens were killed before the July 21 election, which saw weeks of demonstrations, a failed coup and clashes between rebel soldiers and the army.
The weeks of protests and violence has forced more than 175,000 people to take refugee in neighbouring countries.
