The PPP, however, is unlikely to win an outright majority.
The pro-Thaksin party has made bringing the ousted prime minister back from exile its main priority.
Thaksin return
At a campaign rally on Friday, Chalerm Yoobamrung, a PPP parliamentary candidate, said that Thaksin would come home from his self-imposed exile in London on February 14.
But Samak Sundaravej, a party leader and leading candidate for the next prime minister, said that his colleague was joking about the date and that Thaksin would in fact return about a month after the elections.
The PPP, which has embraced populist policies that won Thaksin two landslide victories, urged voters at the rally to bring the toppled prime minister back by giving the party a majority in the 480-seat parliament.
"If the PPP doesn't win more than half, Thaksin can't return," Chalerm told more than 10,000 supporters in Bangkok.
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| Thaksin has urged the people of Thailand to accept the electoral outcome |
In a letter posted on a pro-Thaksin website on Saturday, the former prime minister urged the people to accept the outcome of the election held 15 months after the military removed him.
"We may have had different ideas, but from December 23, I would like to ask my Thai brothers and sisters to bury the hatchet," he said in a statement.
Abhisit Vejjajiva, a leader of the rival Democrat party, alluded to Thaksin in his final speech on Friday, saying a vote for the PPP was a vote for someone who "cheated the nation".
If the PPP wins big on Sunday, analysts expect a blizzard of electoral fraud charges against PPP candidates in the aim of disqualifying them or tying them up in the courts.
The army and its proxies are then likely to push for a coalition government led by the Democrats, the main opposition during Thaksin's five years in power.
Royal concern
Colonel Sunsern Kaekumnerd, a Thai army spokesman, said the army has no preferred candidates for the election.
"No matter who is the next prime minister, or which party runs the country, the army will have no problem…unless that party's intention is to seek revenge," he told Al Jazeera.
But after a shaky year of military rule, many are keen to see the political process return to normal.
The pre-election uncertainty and fears of violence after the poll has worried the country's monarch, King Bhumibol Adulyadej, who made two rare public speeches this week appealing for restraint.
He told judges last week their duty was to remain impartial and preserve justice. On Friday, he urged soldiers and police to use their spiritual "strength" to pull the nation out of its political mess.