
In its verdict, the court noted the gesture to safeguard democracy ended - ironically - by seriously damaging the iconic monument.
It found grounds for leniency and suspended the one-year jail term for two years. It also ordered the three to complete 24 hours of community service within a year.
Chaiyarit Chawiset, Ong-art Wichittranont and Boonsin Yokthip organised a mass rally in November 2007 to protest against the coup staged in September 2006.
As an act of defiance against the power seizure, the three set an effigy of the Constitution on fire, but it got out of control and inflicted about Bt58,700 worth of damage to the monument.
During the trial, which started last December, the three pleaded guilty and agreed to pay for the damage.
The trio was originally sentenced to jail on charges of attempting to resist arrest and recklessness in setting a fire in a public place.
The punishment was suspended because they showed remorse, cooperated with the judicial review and paid compensation for the damage.