A crowd of about 300 supporters and political allies gathered outside the Klong Prem Central Prison to greet the 76-year-old billionaire populist.

Thaksin was a telecommunications magnate who founded his own political party in 1998 and served as prime minister from 2001 until a military coup ousted him in 2006 while he was abroad.

His ouster triggered nearly two decades of deep and sometimes violent political polarisation, while his political machine staged several comebacks even as Thaksin himself stayed in self-imposed exile to escape what he said was political persecution through the courts.

His three children, including former prime minister Paetongtarn Shinawatra, and other family members also arrived early to welcome him.

Thaksin emerged from the prison gate in a white polo shirt and blue pants and was embraced by his family. He smiled brightly as he walked around to greet his supporters who chanted "we love Thaksin," and gave red roses to him. He then left without speaking to reporters.