With nearly all the vote counted, the People's Power Party -- established after Thaksin's Thai Rak Thai Party was disbanded by court order earlier this year -- had won 228 of the 480 seats in the lower house of parliament, according to the state Election Commission. Complete results were due later Monday.
"I would like to call for all political parties to join us in forming a strong government," PPP leader Samak Sundaravej said at a news conference. "I will certainly be the prime minister."
He said Thaksin, who was in Hong Kong, had telephoned to offer his congratulations.
The second-place Democrat Party took 166 seats, while Chart Thai captured 39.
Spokesman Kuthep Saikrajang said the PPP was eyeing Chart Thai and another smaller party as it tried to line up enough seats to form a government. Chart Thai declined to comment on the overture.
"If the PPP succeeds in forming the government, the Democrat Party is ready to be in the opposition to protect the people's interest. However, if the PPP fails to form a government, the Democrat Party is also ready to form a government," said Democrat Party leader Abhisit Vejajjiva.
The PPP got most of its support from the rural north and northeast, where Thaksin's programs, including universal health care and generous village development funds, won a hard-core following.
The Democrats ran strongest in Bangkok, where the 2006 movement to oust Thaksin was centered. Only seven of 39 competing parties won parliamentary seats. About 60 percent of 45 million eligible voters cast ballots for about 5,000 candidates.
If the PPP comes to power, said Nakarin Mektrairat, dean of Thammasat University's Faculty of Political Science, "there will be tension and conflicts," in part because of its lack of support from the capital's residents.
Thai politics has been in almost constant turmoil since early 2006, when protests mushroomed demanding that Thaksin step down, despite his party's landslide victory a year earlier giving it an absolute parliamentary majority.
An April 2006 election was boycotted by the opposition and later declared invalid by the courts, leaving Thaksin's government in limbo until the September 19 coup last year. But the military-appointed interim government that succeeded it proved weak and indecisive, failing to restore public confidence.
Thaksin was abroad at the time of his ouster, and has since stayed in exile. He is legally barred from office, his party has been dissolved by the courts, and he has been charged with a slew of corruption-related crimes.
Despite having vowed retirement from politics, he burnished his image from afar, with such moves as the purchase of England's Manchester City soccer club, buying into the sport's popularity in Thailand.
Thaksin's PPP allies announced last week that he would return to Bangkok early next year, after a new government is installed. Thaksin has not yet commented publicly on the election results.
Despite its victory at the polls, the PPP could face an uphill battle in trying to form a government.
The forces that helped unseat Thaksin -- the military, Bangkok's educated middle class, and the country's elite, including elements associated with the country's monarchy -- have worked hard to erase Thaksin's political legacy.
They changed the constitution to limit the power of big parties and sought to demonize him as a corrupt destroyer of democracy. His return could undo their efforts and put their own positions in jeopardy.
Samak said that, if possible, the PPP would grant amnesty to Thaksin and 110 other executives of his now-disbanded Thai Rak Thai Party, who were barred from office for five years. "They didn't do anything wrong," he said.
Thaksin's allies could see their tally of seats fall by 10-20 as claims of vote-buying are investigated by the Election Commission, which has been hawk-eyed in looking for PPP irregularities. A reduced total from disqualifications would complicate the task of assembling a ruling coalition.
Thailand's long-term prospects for political stability seem poor. Samak, a veteran right-wing politician who has served in several Cabinets and as governor of Bangkok, has been a divisive figure for decades.
The blunt-speaking 72-year-old Samak "doesn't have a conciliatory personality. He is aggressive and uncompromising," said Narong Phetprasert, an economist at Chulalongkorn University.
Critics say Abhisit, 43, British-born and educated at Eton and Oxford, may lack the toughness necessary to keep together a coalition of parties out to get the biggest share of power they can grab.
In Washington, the State Department, which had criticized the coup against Thaksin, said it welcomed reports that the polls were held in a free and fair manner and congratulated the Thai people "on taking this crucial step toward a return to elected government."
Department spokesman Sean McCormack said the U.S. calls on all sides "to respect the results, and for a fair and transparent process for the adjudication of any disputes or fraud claims."