Thailand’s Parliament on Friday picked the 37-year-old heir of a powerful and polarizing dynasty to lead the country, two days after a court ousted the prime minister in the latest blow to Thai democracy.

The lawmakers’ choice of Paetongtarn Shinawatra, a daughter of former Prime Minister Thaksin Shinawatra, as the new prime minister was the latest turn in a political crisis that has roiled Thailand.

Even on Thursday night, as it became clear that Ms. Paetongtarn was the governing coalition’s choice for the role, there were questions about how long she would last. She is not popular: A recent poll found that only 6 percent of voters backed her for prime minister, trailing Pita Limjaroenrat, the former leader of the now banned Move Forward Party, and Srettha Thavisin, the prime minister who was dismissed on Wednesday.

Ms. Paetongtarn’s ascent was the clearest statement yet that Mr. Thaksin, who was ousted from the prime minister’s job in a 2006 coup but has remained a powerful behind-the-scenes player, and his Pheu Thai Party would remain at the forefront of Thai politics.

But she faces numerous challenges, including an ailing economy and a topsy-turvy political era in which the military and its royalist allies have repeatedly disrupted Thailand’s democratic processes.