Socialist MSP Rosie Kane was among a group of 10 anti-nuclear demonstrators fined for blocking part of Edinburgh's Royal Mile in a 15-hour protest.
MSP Rosie Kane was among those fined for causing an obstruction
The demonstrators used a 25ft mock submarine to make their point outside the Scottish Parliament on 10 March.
After a three-day trial at Edinburgh Sheriff Court, they were found guilty of obstructing traffic and the police.
The individuals, representing Trident Ploughshares Movement, were each fined £300 by the court on Monday.
At the start of the court hearing, the Crown withdrew an allegation that the demonstration had placed road users in danger.
Fiscal Malcolm Stewart said the demonstrators claimed they had tried all legal, democratic moves, but said they claimed there was a "democratic deficit" in Scotland and that they could do nothing else but stage the protest.
Mr Stewart said that when asked to move the submarine in the evening and warned that they would be charged, the protesters refused to help and linked arms inside the submarine, which had to be cut apart by police.
The demonstrators all represented themselves and said they had a legal right under international law to protest and had a reasonable excuse.
They claimed the event had been peaceful, friendly and good-natured.
Ms Kane said no-one knew when, where or how Trident missiles might be used.
"We have a duty to let the rest of the world be aware of what we are aware and so they can also make representations to their elected representatives," she said.
Sheriff Noel McPartlin said he took into account the protesters' reasons for acting as they did and conducting themselves in a civilised manner.
He allowed them all three months to pay, although some of them indicated they would not pay the fines.