The presidential election in the archipelago nation was held on January 14.
The Habari Za Comores news website reported that 62.97% of voters had cast their ballots for 65-year-old Assoumani.
Assoumani first came to power in a coup in 1999 after ousting then-President Tadjidine Ben Said Massounde. Three years later, Assoumani resigned to run as a civilian and won the presidential election in 2002. He served as the country's president until 2006, stepped down again and won the election in 2016.
The opposition accused Assoumani of amending the constitution to remain in power until 2029. He also closed the country's Constitutional Court and Anti-Corruption Court. The move forced the European Union to suspend all cooperation with the Comoros.
Assoumani also won the snap presidential election held in March 2019.
The Comoros archipelago, located 155 miles off the southeast African coast, remained a French colony until the mid-1970s. Mayotte, also known as Maore, remained an overseas territory of France following a referendum held in the Comoros in 1974. In March 2009, the island's residents voted in a referendum for the territory to become a French department.