Marc Ravalomanana jailed for four years and fined $70m for “abuse of power”.
Andry Rajoelina, the opposition leader who took over from Ravalomanana after leading protests against him, has called the former president corrupt and dictatorial.
He has established a transitional authority on the Indian Ocean island, and promised an election by 2010.
But many African nations have condemned his takeover as a coup and urged talks between the two rivals.
Ravalomanana is currently in South Africa, where he is seeking international support for a return to Madagascar.