The constitution looked set to pass with 90.6% votes in favor and 9.4% against, Djenabou Toure, head of Guinea's General Directorate of Elections, told reporters. Those figures were based on roughly 91% of votes cast in the referendum.
An overall figure for voter turnout was not available, but officials had counted more than 4.8 million votes out of more than 6.6 million registered voters, meaning turnout had exceeded 70%.
Doumbouya seized power in Guinea, home to the world's largest reserves of bauxite, in 2021. It was part of a wave of eight coups that swept West and Central Africa between 2020 and 2023.
A charter adopted after the coup swept members of the transitional government from seeking office.
But that language was not included in the constitution put to voters on Sunday.
While the referendum has been seen as a step towards elections and the return to civilian rule in Guinea, Doumbouya's opponents have criticized it as a power grab by him.
Doumbouya's government missed a December 31, 2024 deadline it had set itself for a return to civilian rule. Its presidential election is currently expected to take place in December.
Doumbouya, a 40-year-old former member of the French Foreign Legion, voted along with his wife at a health center in Conakry on Sunday, wearing sunglasses and a baseball cap bearing a drawing of a traditional mask symbolizing fertility.