The supplementary election was held in 44 polling units across 14 local government areas of the state after the previous governorship election in the state was declared inconclusive by INEC.
The Returning Officer for the election, Prof. Andrew Haruna, who declared the result early on Friday morning in Yola, the state capital, said that Fintiri polled 376,552 votes to defeat incumbent governor, Jibrilla Bindow, of the All Progressives Congress who got 336,386 votes.
Speaking when he received the Certificate of Return from INEC on Friday at the INEC office, Fintiri commended INEC for conducting what he described as a peaceful, credible and fair election in the state.
He called on the people to join hands with him to address some of the issues confronting the state.
Fintiri pledged to overhaul the security architecture in the state and said that his administration would ensure that people of the state can sleep with both eyes closed, without fear for their safety.
He attributed his victory to the good people of the state and thanked them for giving him the opportunity to serve.
Fintiri was a former Speaker of the Adamawa State House of Assembly in 2014 and served as Acting Governor of the State in July 2014, following the impeachment of the then Gov. Murtala Nyako.
Adamawa State is the home state of the presidential candidate of the PDP, Alhaji Atiku Abubakar.