Thailand's opposition won a landslide election victory on Sunday. Yingluck Shinawatra, Pheu Thai Party's prime ministerial candidate and also the youngest sister of former Prime Minister Thaksin Shinawatra, is set to become the country's 28th and the first female prime minister.

Yingluck said that her party had already made an agreement with Chartthaipattana Party to form a new government.

Exit polls showed that the two parties will win about 278 MPs in the house, well beyond half of total 500 seats, paving the way for the 44-year-old business executive to become the prime minister.

"I'll do my best and will not disappoint you," she told supporters after receiving a call of congratulations from her billionaire brother, who was ousted in a 2006 coup and lives in Dubai to avoid jail for graft charges that he says were politically motivated, Xinhua reported.

Yingluck said "I don't want to announce Pheu Thai victory today. It is Thai people who granted the party a chance to serve them. We still have many burdens waiting ahead, including solving economic difficulties and people's grievances," according to Xinhua.

Meanwhile, Democrat Party leader Abhisit Vejjajiva conceded his party's defeat and congratulated Pheu Thai Party on its decisive victory at about 7:45 p.m. on Sunday.

Abhisit said "I admitted the defeat and would like to congratulate Khun (Ms) Yingluck as the first female prime minister of Thailand."

He said he would like to see reconciliation in Thai society and his party will perform its duty as an opposition in a constructive way. He also reminded the winning party to realize all policies that it promised with the people, Xinhua reported.

Referring to Thaksin, Abhisit reiterated that the Democrats would continue to oppose any act of whitewashing or granting pardon to an individual.

In an interview with ThaiPBS channel Sunday's evening, Thaksin said he would not come back to Thailand if his return would result in more problems.

Yingluck said her premiership depended on parliamentary process. This is the second time she mentioned about the uncertainty of her premiership. On June 27, she told her fan club from social network that she was not sure whether they would allow her to become the country's leader or not.

The size of Puea Thai's victory could usher in much-needed political stability after six years of sporadic unrest that featured the occupation of Bangkok's two airports, a blockade of parliament, an assassination attempt and protests last year that descended into chaotic clashes with the army.

"Chances of blocking Puea Thai in the near term are severely limited," said Roberto Herrera-Lim, Southeast Asian analyst at political risk consultancy Eurasia Group. "The instability everyone has been worried about now looks less likely. The military will have to be pragmatic now," China Daily reported.