He has pleaded not guilty to charges of genocide and crimes against humanity in February, this year.
The accused was transferred to Arusha, Tanzania, on 8 October after a prolonged one-year legal battle in Germany over his trial before the UN Court, trying key architects of the 1994 genocide.
The former Planning Minister was suspected of encouraging the mass murder of members of Rwanda's Tutsi minority by arming the Hutu majority. He was arrested in September, last year.
The accused faces charges of genocide, complicity in genocide, direct and public incitement to commit genocide, crimes against humanity (murder, extermination, rape, inhumane acts) and serious violations of the Geneva Conventions and of Additional Protocol II.
The prosecution claims, among others, that Ngirabatware channeled funds from his ministry to purchase arms "not for national defence, but to arm the civilian population to carry out massacres." Prosecution is expected to field not less than 20 witnesses in scheduled ten days.
The opening was postponed twice, mainly because of unpreparedness of the defence.
Ngirabatware served as Rwanda's planning minister for the four years leading up to the genocide and has since then lived in Gabon and in France for long periods.
He is the son-in-law of most wanted fugitive Felicien Kabuga, who has also been named by the ICTR as a genocide suspect. Kabuga, a wealthy businessman, is alleged to have financed the genocide and suspected to be hiding in Kenya.
The accused was initially jointly charged with Jean de Dieu Kamuhanda, former Minister for Higher Education and Scientific Research who in January 2004 was convicted and sentenced to imprisonment for the remainder of his life, following dismissal of his appeal on 19 September 2005.
According to the United Nations estimates, about 800,000 ethnic Tutsis and moderate Hutus were killed in the April-July 1994 slaughter.
© Hirondelle News Agency