Former prime minister Thaksin Shinawatra bowed in homage to the Thai king's portrait as he returned to the kingdom on Tuesday after 15 years in exile.

Thaksin, 74, paid his respects to King Maha Vajiralongkorn and waved in greeting to hundreds of supporters gathered at Bangkok's Don Mueang airport before being led away by officials to be processed on multiple outstanding criminal cases.

The former Manchester City owner faces immediate arrest on old criminal cases, in the latest act in the kingdom's rolling political drama.

Lawmakers will vote in the afternoon to install business tycoon Srettha Thavisin as prime minister at the head of a coalition led by the Pheu Thai party – the latest incarnation of Thaksin's political movement.

Earlier, a Facebook video posted by his sister Yingluck – like Thaksin, ousted from power by Thailand's generals – showed the 74-year-old shaking hands with the crew as he boarded his jet in Singapore.

"The day you are waiting for is finally come," Yingluck wrote.

A day that began with a private jet for Thaksin will likely end in a prison cell – yet another dramatic shift in a switchback career that has included two election victories, defeat in a coup, criminal charges and long years of self-imposed exile.

Thaksin has said he is prepared to face justice in order to return to his homeland and see his grandchildren – though he has long maintained the criminal charges against him are politically motivated.

"I would like to request permission to return to live on Thai soil and share the air with my fellow Thai brothers and sisters," he posted on Twitter, which has been rebranded as X, on Monday.

At the airport, hundreds of supporters from the "Red Shirt" movement loyal to Thaksin gathered singing songs and waving banners – most decked out in their usual crimson colours.

The former prime minister has been convicted in four criminal cases in his absence, although the statute of limitations has expired in one. The jail sentences against him total 10 years. (AFP)