Yingluck, sister of fugitive former premier Thaksin Shinawatra, retained an air of calm confidence after she on Friday won a parliamentary vote to become premier with the support of 296 members of the lower house out of a potential 500.
The country's 28th prime minister, who was catapulted from relative obscurity to election victory by her older brother's support, can expect royal endorsement within days to formalise her position.
"I am excited to start work," she told reporters after the vote. "People will judge whether my work satisfies them and meets their expectations or not."
Yingluck's Puea Thai party and its partners command a three-fifths parliamentary majority after a resounding victory in the July 3 election over the pro-establishment Democrats.
The 44-year-old surprised observers with her assured campaign style and she has since consolidated her parliamentary dominance by forming a six-party coalition that accounts for 300 of the legislature's 500 seats.
Yingluck, described by her brother as his "clone", on Friday again rejected suggestions that Thaksin, who lives abroad to avoid a jail term for corruption, is controlling her party from afar.
Asked if she was in contact with her brother, she replied: "No, I am not talking to anyone."
Thailand has seen a period of instability since Thaksin, the only prime minister in the country's history to win a second term, was removed from power in a 2006 military coup backed by Thai elites.
A group of around a hundred of his "Red Shirt" supporters gathered outside the parliament building ahead of the vote on Friday morning, many wearing their signature coloured tops bearing pictures of Yingluck's face.
Yingluck is expected to face pressure from the mainly poor and working class Reds, many of whom support Thaksin for his populist policies during his 2001-2006 rule.
The movement, which has key representatives in Yingluck's party, will expect justice over its April and May rallies last year that ended with a military assault and more than 90 people dead.
Analysts believe a key test for the fresh-faced political newcomer will simply be whether she can hang on to power in a country where the removal of leaders is commonplace.
Thailand has seen 18 actual or attempted military coups since it became a constitutional monarchy in 1932 and only one prime minister in that time has served a full four-year term – Thaksin.
"We are still in the middle of a very big conflict in the country with very different ideas about what government should be, and what it should be doing," said Thai political analyst Chris Baker.
Baker said her parliamentary majority – along with the weakened state of the nationalist and anti-Thaksin "Yellow Shirt" protest movement and a lack of public support for the army – will give Yingluck "breathing room".
Vote-grabbing promises, such as a minimum wage hike and higher rice prices for farmers, were a nod to Thailand's less economically fortunate, but the Bank of Thailand warning they could stoke inflation.
Yingluck, who said she would work on finalising her cabinet over the weekend, said her first thought would be the poorer in society.
"Our first priority is to solve the high cost of living for people," she said.