Thai Rak Thai was dissolved by court order after the 2006 coup but eventually evolved into the Pheu Thai party, which brought Thaksin’s sister Yingluck to power in 2011.
Thaksin is seen by many as the true master of Pheu Thai, which came second in May’s general election and is set to lead a new coalition government.
Yingluck laboured under claims she was a Thaksin stooge and eventually, she too fell to a coup.
From exile in Dubai, divorced Thaksin regularly took to the Clubhouse social media platform under the moniker “Tony Woodsome” to address supporters in Thailand.
Over the past year, he has thrown his weight behind his daughter Paetongtarn Shinawatra as she took up the Pheu Thai mantle and led the party’s election campaign.
He is believed to be particularly close to Paetongtarn, 37, and has said his main motivation for returning to Thailand is to spend time with his grandchildren.
But first, he faces the prospect of prison after being convicted in his absence in several criminal cases and sentenced to 10 years in jail.
After years of saying the charges were politically motivated, Thaksin now says he is willing to face justice – though rumours have swirled of a deal for leniency and it is not clear how long he will serve.
The decision to return came after Pheu Thai made what many see as a Faustian bargain to go into coalition with military-backed parties – including the ex-army chief who ousted Yingluck in 2014.
The deal has enraged some supporters.
“This is a betrayal for Red Shirts people who have fought against the establishment,” Jatuporn Prompan, a former leader of the “Red Shirt” pro-Thaksin protest movement, told AFP.