Thailand's most famous politician made a dramatic homecoming last month, 15 years after he entered self-exile, having been ousted by a military coup in 2006. While abroad, Thaksin was found guilty in absentia in three cases involving abuse of power, conflict of interest and malfeasance.
His return to Thailand coincided with emergence of his ally Srettha Thavisin as the country's new prime minister, following months of uncertainty in the wake of an election in May that resulted in defeat for the ruling pro-military party.
Parties aligned with Thaksin have won every election since 2001 up until this year's poll when the Pheu Thai, the party backed by his family, came second.
The telecommunications billionaire, whose brash personality and populist policies appealed to poorer Thais, clashed with the country's old money elites and royalist military, which also ousted his sister's government in 2014.
There was speculation that Thaksin reached some deal with his old foes, after the pro-military parties gave the Pheu Thai candidate Srettha their backing to form a new government.
Thaksin and Srettha deny this.
On his first night in Thailand, Thaksin was transferred to a police hospital with chest pains and high blood pressure where is currently being treated.
Days later, King Maha Vajiralongkorn commuted his eight-year sentence to one year, but he could be released sooner.
"After serving six months of his sentence, Thaksin will be eligible for parole for prisoners older than 70 or those who are ill," Corrections Department Deputy Director General Sitthi Sutivong, told Reuters.
The corrections department makes an assessment for each case and there is no petition process for parole in these cases, he said.
The former prime minister's treatment in hospital is at the discretion of medical professionals and does not have a time limit, Sitthi added.