Samak Sundaravej, leader of the PPP, told a news conference on Sunday evening that he would form a coalition after falling short of a full majority.
The military-backed Thai government dissolved the TRT and banned Thaksin from politics for five years after they seized power in a bloodless coup in September 2006.
But though he lives in self-imposed exile in London, Thaksin remains a dominant figure in Thai politics.
Analysts say the outcome of the election is unlikely to resolve divisions between Thaksin's supporters, largely drawn from the rural masses, and those ranged against him.
Panitan Wattanayagorn, from Thailand's Chulalongkorn University, said:
"People are expecting that the return of democracy is going to take place today.
"Although the new government is expected to be a coalition government, comprising of at least two or three more parties.
"No one is expecting one single party to win the election today. In a house of 480 seats, no one single party will likely gain more than 240 seats in this election."
The PPP draws most of its support from farmers, the majority of Thailand's 64 million population, who remember Thaksin's efforts to boost the rural economy.
The party has embraced the policies that won Thaksin two landslide victories and intends to bring him home if it wins a majority in parliament.
"If the PPP doesn't win more than half, Thaksin can't return," Chalerm Yoobamrung, a PPP parliamentary candidate, told more than 10,000 supporters at a rally in Bangkok on Saturday.
Clear winner unlikely
Al Jazeera's Tony Cheng, reporting from Bangkok, Thailand's capital, said a clear winner will not be seen.
He said: "If a representative of a smaller party becomes the next prime minister, it may create confusion in a country still sharply divided among supporters and opponents of Thaksin Shinawatra."
People Power Party
The party is led by 72-year-old Samak Sundaravej, six-time cabinet minister under investigation in two corruption cases from his time as governor of Bangkok.
The party is campaigning on a platform of cheap health care, low-interest loans for the poor and greater funds into village-level development.
It has pledged to bring home Thaksin Shinawatra, the exiled former prime minister.
Thailand's oldest party is led by 43-year-old, Oxford-educated Abhisit Vejjajiva, who has been a member of parliament for 16 years.
He has been criticised for not connecting with poor, rural voters.
The party promises free education, a focus on resolving the four-year Muslim insurgency in the country's south and rooting out corruption.
For his part, Wattanayagorn said: "The next government will have to deal with at least three or four central issues.
"It may have to amend new rules, the new constitution and may have to come up with new, more democratic institutions. That is the first challenge.
"They need to also deal with the remaining corruption charges of several executives in the political parties. That has to be smooth and stable in order to provide a stable government.
"The other challenge is to revive the economy, to make sure that Thailand's economic growth is more than four per cent or five per cent compared to their neighbouring countries.
"And, lastly, the new government must deal effectively with the violence in the three southern provinces."
In August, a referendum ratified a new, army-backed constitution to replace Thailand's 1997 constitution, widely held to be the most democratic the kingdom had seen.
The new constitution paved the way for Sunday's election.
Nevertheless, critics caution that the charter will encourage weak coalition governments while returning real authority to the military, the bureaucracy and the royal palace.
General Sonthi Boonyaratglin, the leader of the 2006 coup, has said he will respect the outcome of the election.
The polls are meant to return power from the military to civilian rule, with unofficial results expected by midnight on Sunday.