With Adeeb's sentencing, almost all of President Abdulla Yameen's key rivals are either in jail or living in exile.
The tiny nation of 340,000 Sunni Muslims has been gripped by political turmoil since Nasheed -- its first democratically-elected president -- was toppled four years ago in what he claimed was a coup led by mutinous police and troops.
Nasheed -- whose legal team includes high-profile human rights lawyer Amal Clooney -- was sentenced to 13 years on controversial terrorism charges last year but was allowed to travel to Britain for surgery last month and was granted political asylum.
"It is an unfair trial and we will appeal against the verdict at the High Court," Siraj told reporters in Male.
A court official said the case record will not be released to the public as it was considered a matter affecting national security.
Adeeb, 34, once a close confidant of Yameen, had enjoyed a meteoric rise until he was dramatically impeached in November after being accused of trying to assassinate his boss by blowing up his speedboat.
Nearly four months ago, Yameen secured the jailing of another dissident, Sheikh Imran Abdulla, leader of the opposition Islamist Adhaalath Party.
He was jailed for 12 years after being tried under a controversial 1990 anti-terrorism law for allegedly inciting unrest during an anti-government rally in May 2015 on the capital island.
Imran's party had joined the main opposition Maldivian Democratic Party (MDP) last year at a mass rally to protest the jailing of dissidents, including Nasheed.
Yameen has invited opposition parties for talks to resolve their differences, but they have ended in failure.
