Thailand's governing alliance agreed on Thursday to back 37-year-old political newcomer Paetongtarn Shinawatra as its candidate for prime minister, a day ahead of a pivotal vote in parliament.

The deal follows a flurry of behind-the-scenes talks in the 24 hours since a court dismissed Srettha Thavisin as premier, as his Pheu Thai Party rushed to secure backing from its 11-party alliance in a bid to form the next government.

Paetongtarn is the daughter of divisive political heavyweight Thaksin Shinawatra, and a niece of Yingluck Shinawatra, both former premiers who fled into exile after military coups against their governments.

Wednesday's dismissal of Srettha by the Constitutional Court was the latest hammer blow for Pheu Thai, the populist electoral juggernaut of the billionaire Shinawatra family that has locked horns for two decades with Thailand's influential establishment and royalist military.

If successful in Friday's vote, Paetongtarn would be Thailand's second female prime minister and the third Shinawatra to hold the top post.

"We were confident that under her leadership, we will all support her and be ready to carry out her policies from the day she assumes office," Anutin Charnvirakul, leader of the Bhumjaithai Party, told a press conference to announce Paetongtarn as candidate.

Srettha was the movement's fourth premier to be removed by a court ruling and his downfall could indicate the end of an uneasy detente between Thaksin and his enemies in the conservative elite and military old guard, which had enabled the tycoon's return from self-exile in 2023 and ally Srettha to become premier the same day.

The 11-party alliance holds 314 seats in the house, of which 141 belong to Pheu Thai, and should have no difficulty electing a prime minister on Friday, providing it remains intact.

To become premier a candidate needs the approval of more than half of the current 493 lawmakers.