A decree by the Council of Ministers announced the "convening of the electoral college for the election of the President of the Republic" plus members of the national assembly and municipal councils, on Saturday, August 26.
President Ali Bongo Ondimba has not yet said whether he will stand again, but he is widely expected to run for re-election.
His Gabonese Democratic Party (PDG) holds strong majorities in both houses of parliament and is pushing for the president to announce he will stand again.
In 2009, the now 64-year-old Bongo took over from his father Omar Bongo Ondimba, the oil-rich country's ruler for 41 years.
The president was re-elected in 2016 with 5,500 votes more than rival Jean Ping.
In April, the Gabonese parliament voted to amend the Constitution and reduce the president's term from seven to five years.
The amendments bring all mandates in line at five years and make all elections single-round ballots again after the last changes to the Constitution in 2018 set up two rounds of voting.