The ruling adds more jail time to the 17 years she is already serving for other offences.
It also imperils the survival of Suu Kyi's National League for Democracy party following the government's explicit threats to dissolve it before a new election the military has promised will take place in 2023.
Suu Kyi's party won the the 2020 general election in a landslide victory. But the military seized power from Suu Kyi's elected government on February 1 2021, saying it acted because of alleged widespread voter fraud.
Independent election observers did not find any major irregularities.
Two senior members of Suu Kyi's former government were co-defendants in the case and also received three-year prison sentences.
Myanmar has been in the grip of a ruthless cabal of senior military officers determined to maintain a hold on power.