Bizimungu was appealing a sentence imposed in May 2011. He is among the most senior figures to be tried by the Tanzania-based tribunal for the genocide in which 800,000 people, mostly Tutsis, were killed.
The court found Bizimungu had complete control over the men he commanded, who were involved in the massacres that started in the night of April 6, 1994.
It also found him guilty of making a speech the following day in which he called for the killing of ethnic Tutsis, just a few days before he was made army chief.
Bizimungu claimed during his appeal hearing that he had “urged military discipline and respect for the dignity of human life.”
But prosecutor Abdoulaye Seye asked for a heavier sentence.
The ICTR, based in the northern Tanzanian town of Arusha, was established in late 1994 to try the perpetrators of Rwanda’s genocide.
It is tasked only with trying those who bear the greatest responsibility for the genocide, but is now wrapping up its work.
Less senior officials and ordinary citizens accused of taking part have been tried in Rwanda.