Thailand's parliament elected political neophyte Paetongtarn Shinawatra as its youngest prime minister on Friday, only a day after she was thrust into the spotlight amid an unrelenting power struggle between the country's warring elites.

The 37-year-old daughter of divisive political heavyweight Thaksin Shinawatra sailed through a house vote and now faces a baptism of fire, just two days after ally Srettha Thavisin was dismissed as premier by a judiciary central to Thailand's two decades of intermittent turmoil.

At stake for Paetongtarn could be the legacy and political future of the billionaire Shinawatra family, whose once unstoppable populist juggernaut suffered its first election defeat in over two decades last year, and had to do a deal with its bitter enemies in the military to form a government.

She will become Thailand's second female prime minister and the third Shinawatra, opens new tab to take the top job after aunt Yingluck Shinawatra, and father Thaksin, the country's most influential and polarising politician.

In her first media comments as prime minister-elect, Paetongtarn said she had been saddened and confused by Srettha's dismissal and decided it was time to step up.

"I talked to Srettha, my family and people in my party and decided it was about time to do something for the country and the party," she told reporters.

"I hope I can do my best to make the country go forward. That's what I'm trying to do. Today I'm honoured and I feel very happy."

Paetongtarn won easily with 319 votes, or nearly two-thirds of the house. Her response after winning was posting on Instagram a picture of her lunch - chicken rice - with the caption: "The first meal after listening to the vote."