Bizimungu, whose trial began on 1 April, was convicted on Monday of attempting to form a militia group, inciting violence and embezzlement, receiving a consecutive five-year jail sentence for each. He had denied all charges.
An ethnic Hutu, Bizimungu became president when the ruling Tutsi-dominated Rwandan Patriotic Front (RPF) took power in 1994 after the genocide in which extremists from the Hutu majority butchered 800,000 Tutsis and politically moderate Hutus.
Paul Kagame, whose Tutsi-led RPF ended the 100 days of slaughter, was vice-president.
The double-act of Bizimungu, a French-speaking Hutu, and Kagame, an English-speaking Tutsi, was intended to symbolise post-genocide reconciliation.
However, their relationship soured, and in March 2000, Bizimungu resigned after falling out with top RPF members.