The electoral commission in Guinea says the party of President Alpha Condé won more than two-thirds of the seats in last month’s parliamentary elections, which the opposition boycotted.
The government had already declared victory in a referendum held the same day about changing the constitution, which would allow Mr Condé to seek a third term in office.
The adoption of the new constitution means that time Mr Condé has already served does not count – and his second term comes to an end in December.
Mr Condé, who is 82, has argued that constitutional changes are needed to usher in social reforms, especially to benefit women.
The question of constitutional change in Guinea has provoked months of unrest, leading to several dozen deaths.