Sheikh Imran Abdulla, the leader of Islamist Adhaalath Party, was sentenced late on Tuesday for an anti-government speech he made during a massive protests against Nasheed's arrest on May Day last year.
Imran's lawyer Husnu Suood said it was the first terrorism conviction based on a speech in the history of the Maldives.
"We believe the judgment is grossly unfair because he has not called for violence in his speech. He clearly asked the participants at the rally to refrain from violence and had taken all steps to prevent violence," Suood told Reuters.
The sentence comes days after Maldives President Abdulla Yameen called on the opposition parties to end a standoff with his own party amid rising international pressure.
Adhaalath Party Spokesman Ali Zahir said the sentencing demonstrated the absence of good faith from the government's side in the inter party talks.
Nasheed, who freed from jail last month to seek medical treatment in London, has called for sanctions against Yameen and his allies for detaining political prisoners, mainly opposition leaders.
Political unrest in the archipelago has continued since Nasheed was ousted in disputed circumstances in February 2012. He was then arrested and sentenced in March for ordering the abduction of a judge, following a rapid trial that drew international condemnation.
Thousands took to the street for the May Day protest calling for the release of former president, who was sentenced to 13 years in jail after also being convicted on terrorism charges. Hundreds of his supporters were arrested in clashes with police.