Rwanda has pardoned more than 2,000 prisoners, including a top opposition figure, BBC reports.
Victoire Ingabire, of the FDU-Inkingi party, has been serving a 15-year jail term for threatening state security and “belittling” the 1994 genocide.
She has been a leading critic of President Paul Kagame and says her trial was politically motivated.
Mr Kagame has won praise for reforming Rwanda’s economy but has also been accused of human rights abuses.
He won re-election for a third time last year with 98.8% of the vote, in what election observers said was a sham.
The release of Ms Ingabire and 2,140 other convicts was announced by the government following a cabinet meeting.
No reason was given for the move, but a statement said that Mr Kagame had exercised mercy under his prerogative as president.