Patongtarn, 36, has attended party rallies in the past year and in recent months has led opinion polls on top prime ministerial candidates, far ahead of incumbent Prayuth Chan-ocha, who led Yingluck’s government as army chief. was uprooted.
Yingluck and Thaksin are both living abroad to avoid prison sentences under military rule.
Prayuth has been in charge since 2014, initially as junta leader and then elected by parliament after the 2019 election as prime minister, something his critics say was held under rules designed to keep him in power. He insisted that he earned the role fairly.
Prayuth, 68, joined the new United Thai Nation party last week, showing signs of staying on as premier.
They have yet to dissolve parliament and elections should be held by May.