Tsikhanouski's sudden release came as US special envoy Keith Kellogg visited Belarusian capital Minsk on Saturday and held a meeting with the country's authoritarian leader Alexander Lukashenko.
Kellogg's deputy John Coale said in a post on X that a total of 14 prisoners had been released in an agreement helped through the cooperation of the Lithuanian government.
Speaking at the US embassy in Vilnius, Lithuania, Coale said that Kellog's visit to Belarus had the full approval of President Donald Trump.
Lukashenko, the Belarusian strongman leader, has been isolated by Western politicians for many years. Neither his 2020 re-election nor this year's were officially recognised, and Belarus remains under Western sanctions.
The freeze in relations deepened when Belarus aided Russia in its full-scale invasion of Ukraine, allowing troops to cross its territory and missiles to be launched from its land.
But the release of Tsikhanouski and other prisoners does not mean the end of political repression in Belarus.
Hundreds more people are still behind bars for nothing more than their opposition to Lukashenko's rule.
Tsikhanouski was imprisoned in May 2020 as he prepared to run for the presidency against Lukashenko.
Tsikhanouskaya ran in her husband's place in the presidential election. Mass protests broke out in the country after the opposition accused Lukashenko of rigging the vote in August 2020.
Tsikhanouskaya said in December 2021 that her husband, who denied the charges against him, had been sentenced to 18 years in prison.
(ab/gs)
Click on the audio player above for a report by Agnieszka Bielawska.