Veera, a coordinator of the Thai Patriots Network and a former yellow-shirt leader, was granted a royal pardon, the Phnom Penh Post quoted the Cambodian prime minister's spokesman as saying.
“Veera will be released [Tuesday] through a royal pardon from King Norodom Sihamoni and will accompany [Thai acting foreign affairs minister] Sihasak [Phuangketkeow] and his delegation back to Thailand" on Wednesday, said Eang Sophalleth, spokesman of Prime Minister Hun Sen.
The group is expected to touch down at Suvarnabhumi airport at 11am Wednesday on flight PG938.
The pardon was accompanied by a request from Hun Sen that the Thai junta release 14 Cambodian migrant workers jailed earlier this month after they were caught with fake visas, the Post said.
Political analysts predicted a prisoner swap between the two nations was possible.
“This is a win-win type of deal for both sides,” Thai politics expert Kevin Hewison told the Phnom Penh Post last week.
“They’ll both be seen as doing good by their constituents without having to lose anything,” he added.
Mr Sihasak said Hun Sen understood Thai politics and reiterated Cambodia would not interfere or support anti-coup movements.
Veera, together with his secretary Ratree Pipattanapaibul and five other Thais, was arrested in December, 2010, while inspecting a "disputed" border near Ban Nong Chan village in Sa Kaeo’s Khok Sung district. It was Veera's second arrest along the border, after he had signed a promise in Cambodia not to approach the border again.
He was sentenced in May, 2011, for illegal entry, spying and entering a restricted military zone without permission.
Veera and Ratree were given jail terms of eight and six years respectively.
Ratree was granted a royal pardon in February. 2013.