The Supreme Court's Criminal Division for Holders of Political Positions has judged former prime minister Somchai Wongsawat and three other defendants not guilty over the forceful dispersal of yellow-shirt protesters in 2008.
The court ruled on Wednesday that Mr Somchai, who was then prime minister, his deputy prime minister Chavalit Yongchaiyudh, then-national police chief Pol Gen Patcharawat Wongsuwon and then-metropolitan police commander Suchart Mueankaew performed their duty in clearing the way for the cabinet members and MPs to leave the parliament on Oct 7, 2008.
The four men were charged with abuse of authority in 2015 by the National Anti-Corruption Commission. All denied the allegations.
The legislative house was blockaded by members of the People's Alliance for Democracy against Dictatorship, who moved there from their occupation of Government House on that day.
They hoped to prevent Mr Somchai delivering his policy announcement after he had succeeded Samak Sundaravej, who was forced to resign the premiership.
Mr Somchai and his cabinet managed to go inside, but the protesters returned again in the afternoon to prevent them leaving the parliament grounds.
Cabinet members had to leave via the rear of the compound, using ladders to climb over fence.
The crackdown began in the afternoon to clear the way for other MPs and officials to leave the parliament.
Two protesters died and 417 were injured during the crackdown, as the protest became violent when police used tear gas to disperse them.
The court said authorities had no intention of causing injuries or loss of life when they launched the operation to clear away the protesters.
Before entering the court house to hear the judgement, Pol Lt Gen Suchart said he would respect whatever decision the court made. The others made no comment.