Polling has ended in Thailand's controversial general election, which was boycotted by the three main opposition parties.
Mr Thaksin called the poll three years early
PM Thaksin Shinawatra hopes the election will strengthen his position.
But both the opposition and leaders of the anti-Thaksin rallies that have become a regular event in Bangkok urged people to register a protest vote.
Three bombs have exploded at polling stations in the mainly Muslim far south, wounding at least five people.
Ballots are being collated from the 87,000 polling stations across 76 provinces.
Preliminary results will be available later on Sunday but full official results are not expected until Tuesday, the Election Commission says.
Mr Thaksin says he will step down if his party fails to win 50% of votes.
Voters have the option of registering a "no vote" if they do not want to vote for a ruling party candidate.
The boycott by the three main opposition parties meant that candidates from Mr Thaksin's Thai Rak Thai party stood unopposed in many seats.
According to the Thai constitution, all 500 parliamentary seats must be filled for the lower house to convene, but in some seats unopposed Thai Rak Thai candidates are unlikely to achieve the 20% of the vote necessary to be accepted as legitimate MPs.
Although voting was largely peaceful, three bombs exploded at polling stations in the far southern Narathiwat province, injuring at least four policemen and a soldier.
The bombs went off about 20 minutes after polling closed, police said.
Thailand has three Muslim-majority provinces in the south where a separatist insurgency has claimed more than 1,300 lives since January 2004.
Shin Corp row
About 45 million people were expected to vote in the election, which is compulsory.
Mr Thaksin called it three years early to try to end months of street protests sparked by accusations against him of corruption and abuse of power.
Three bombs went off in the mainly Muslim far south
Mr Thaksin voted just a couple of hours after the start of the poll.
"This election is very important for the direction of the country because there is a split right now," he said.
The anti-Thaksin movement urged people to wear black armbands while voting.
Student Saritdet Bunsakun, said: "This election is meaningless. I just wanted to exercise my right to vote."
The movement says it will keep up its protests against Mr Thaksin whatever the election outcome.
The prime minister told the BBC on Friday he had voter support and denied any wrongdoing over the sale of telecoms company Shin Corp by his family, which has stirred the political crisis.
Critics say the family avoided tax on part of the sale and are angry about the transfer of control of an important Thai company to Singaporean investors.
But Mr Thaksin said he was not involved in practical aspects of the company and defended the actions of his family.
On Friday, a last-ditch bid to have Mr Thaksin disqualified from the elections over alleged violations of campaign law failed when the Administrative Court refused to hear a petition from anti-Thaksin campaigners.