They are accused of trying to oust the government of the then premier, pro-Western Milo Djukanovic.
Andrija Mandic and Andrija Mandic, both from the Democratic Front, were charged along with two Russians, nine Serbian citizens and one other Montenegrin, the court in Podgorica announced.
They are accused of trying to oust the government of the then premier, pro-Western Milo Djukanovic, in an effort to prevent Montenegro from joining NATO.
Montenegro's special prosecutor has said "Russian state bodies" were involved in the thwarted attack -- an allegation strongly denied by Moscow. But Washington said Wednesday that it had seen credible reports of Moscow's backing.
A group of Serbian nationals were arrested on the eve of Montenegro's election in October, and nine have already been sentenced to a few months in jail after agreeing to testify and striking a deal with prosecutors.
Mandic, who insists the coup bid was staged to discredit his party, on Thursday denied any criminal wrongdoing.
"This is a political trial set up to weaken the Democratic Front and to allow the regime to settle its accounts with the opposition," he said after the indictment was made public.
He added however that they would respond to a court summons, even though "we do not trust Montenegrin institutions".
He and his co-accused are charged with "criminal association" with a view to "committing terrorist acts" and undermining the constitutional order, according to the court statement.
The two indicted Russians -- who are at large -- are accused of organising the plot and being Russian agents.
The plotters intended to "commit an undefined number of terrorist acts" aimed at "permanently destabilising Montenegro and seizing power," the court statement said.
Montenegro is on the brink of joining NATO after Washington signed off on its accession this week, but membership of the Western alliance remains a divisive issue among the 620,000 citizens of the ex-Yugoslav republic.
Another Democratic Front leader, Predrag Bulatovic, said they would organise protests to demand fresh parliamentary elections, but not to pressure the courts.