However it is now looking more likely that the pro-military party will be in a position to form a government under the current leader, General Prayuth Chan-ocha, who led the coup that ousted Mr Thaksin's sister Yingluck Shinawatra in 2014.
It had racked up more than 7.6 million votes with more than 90 percent of ballots tallied, giving any government it tries to form a claim to legitimacy.
Led by telegenic billionaire Thanathorn Juangroongruangkit, Future Forward took more than five million votes, which could make it Thailand's third-biggest party.
"This will leave the pro-military government with a large, strong opposition that's led by Pheu Thai and Future Forward - both staunch critics of the junta", said Punchada Sirivunnabood, an associate professor in politics at Mahidol University.
The Lower House and the upper house, the Senate - which is appointed entirely by the ruling junta - will together select the next Prime Minister.
The main opposition Pheu Thai party and its previous iterations have won every election since 2001, and is again tipped to win the most seats in the lower house this time round, but not enough to form a government, observers noted.
Speaking to The Straits Times on the phone from Hong Kong on Monday (March 25), Mr Thaksin said he believed both the Thai and worldwide community "know very well (the) irregularity of the result and the irregularity of how the Election Committee of Thailand (ECT) behaved".
Thaksin was ousted in a 2006 military coup and now lives in exile overseas to avoid a prison term, but parties allied with him have won every election since 2001.
NZ to hold national remembrance for Christchurch
Thank you to the New Zealand Prime Minister for your leadership among all the people of New Zealand and to show love towards the Muslim community.
"Under democracy, whoever wins, has the wish of the people, can form the government".
From 8am to 5pm (9am to 6pm Singapore time), around 51 million voters will cast a single ballot for their preferred constituency candidates.
He sidestepped questions over wildly inaccurate poll returns reported late Sunday in several constituencies, as down to "human error".
"There is suspicion about extra ballots where the number of ballots was higher than the number of voters in some districts", said Pheu Thai Party spokesperson Ladawan Wongsriwong.
Shares in Thaksin-linked companies fell on Monday amid concerns that Pheu Thai had fared worse than expected in the election.
In the end, voter turnout was far lower than expected at just over 65%, which is thought to have hurt the pro-democracy parties.
Unofficial results show the military-backed Palang Pracharat party won the popular vote.
Pheu Thai, which was ousted from power in 2014 and is allied with the exiled Thai leader Thaksin Shinawatra, fell well short of the landslide victory that its supporters had hoped for.
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He added: "Everyone knows Shaquille O'Neal, they know I'm in the fun business, and we want to get this thing back on track". O'Neal said in an interview on CNBC Friday that Schnatter's use of the slur hurt the brand with African-American customers.
The official election results do not have to be declared until May 8.
"As long as we still have breath, we can not give up", he said in a Facebook post on today.
The military's party emulated Thaksin's populist formula in a bid to win more votes, proposing lower taxes, a minimum wage increase of more than 30%, and guaranteed prices for rubber, rice, and sugar cane.
"Everyone knows in Thailand, everyone worldwide that observed the election in Thailand, knows that (there) are irregularities", he told AFP in English. "It's not good for Thailand".
It was not clear how many seats Palang Pracharat would have in the House of Representatives, as the Election Commission said it would only release the winners of 350 seats on Monday. The commission said on Monday it will announce the official results of the final 150 seats in the 500-seat parliament on May 9.
Another royal command in February torpedoed the candidacy of the king's elder sister Princess Ubolratana for prime minister of a party linked to Thaksin.
The vote is taking place under a military-backed constitution, Thailand's 20th.
Meanwhile, the Palang Pracharat party is all but guaranteed the support of the junta-appointed Senate, under new electoral rules the junta drafted.
Obama's March Madness Bracket Has A UNC-Duke Final
He has No. 1 Gonzaga facing No. 4 Florida State in the Sweet 16, calling for the Seminoles to upset the Zags again. As far as a Final Four representative I look for 2nd seed MI to advance but this region could be full of upsets.