Former Rwandan President Pasteur Bizimungu has lost his appeal against a 15-year jail term imposed in 2004.
After his resignation, Bizimungu became a vocal government critic
During the appeal, the country's first post-genocide president had told the Supreme Court his arrest and conviction were "politically motivated".
He was arrested in 2002 after trying to form a political party and convicted for embezzling state funds, inciting violence and criminal association.
A BBC correspondent in Kigali said the courtroom was packed for the ruling.
The Supreme Court also rejected the appeal of former Transport Minister Charles Ntakirutinka, but acquitted six other co-accused colleagues.
The BBC's Geoffrey Mutagoma says Mr Bizimungu was in court wearing a black suit.
The courtroom was so full it was difficult to see his reaction as the court upheld the convictions, our reporter says.
Mr Ntakirutinka's wife said afterwards she was not surprised by the decision.
After his arrest in 2002, the authorities accused the former president of stirring up divisions between Tutsis and the majority Hutus.
During the appeal he said it was unfair for him to be convicted on charges different to those for which he was arrested.
Mr Bizimungu was one of only a handful of Hutus to join the Rwandan Patriotic Front (RPF), the rebel movement formed among Tutsi exiles in Uganda.
The RPF took control of Rwanda in July 1994, putting an end to the genocide organised by extremist Hutu leaders that left about 800,000 Tutsis and moderate Hutus dead.
But after his resignation in 2000, Mr Bizimungu became a vocal critic of the RPF-led government.
While the RPF says it has introduced stability and multiparty democracy, its critics claim it has centralised power within a Tutsi elite and crushed potential opponents - by accusing them of promoting ethnic divisions.