Justice Minister Somsak Thepsutin has signed an order for the early release of 76 prisoners who received royal clemency, but they will have to wear electronic tags.
They include United Front for Democracy against Dictatorship co-leader Nattawut Saikuar, of the red-shirt movement.
Justice deputy permanent secretary Witthaya Suriyawong said the minister signed the document on Friday. The 76 prisoners would be released on suspended jail terms
All would be fitted with electronic monitoring bracelets at the Probation Offices in their provinces before being allowed to go home.
Mr Witthaya said Mr Nattawut would wear a bracelet to monitor his behaviour in Bangkok after he leaves Bangkok Remand Prison.
The red-shirt frontman was sentenced in June to two years and eight months in jail by the Supreme Court for leading a violent protest outside the residence of late Privy Council president Prem Tinsulanonda in 2007. The court reduced the lower court's sentence of four years and four months.
He was among prison inmates who received royal clemency on the birthday of the late King Bhumibol, Dec 5, which is also Father's Day.
A group of his supporters were waiting outside Bangkok Remand Prison on Friday, expecting him to be allowed to walk out.
Prisoners who are not being released but whose prison terms were reduced included former TV anchor Sorrayuth Suthassanichina and former commerce minister Boonsong Teriyapirom.