The Appeals Court Region 2 freed Arisman and 12 others after they posted Bt2 million in cash as bail.
The 13 red shirts were found guilty on Thursday of laying siege to the venue of the Asean Summit in Pattaya in 2009 and were each sentenced to four years in jail.
They embraced their loved ones and other red shirts |who were waiting outside the prison to be reunited with them.
Arisman said the release was a great victory for people who had worked for the country and for democracy.
“Throughout the time we spent in jail, we thought that we must sacrifice and we must endure the pain, otherwise there will be no democracy. Thanks everyone for giving us moral support and thanks to the court for giving us justice,” he said.