Yingluck last week refused to postpone the election, even though a fifth of those registered for advance voting were unable to cast ballots after protesters blocked polling stations in 49 of 50 Bangkok districts as part of a "shutdown" of key intersections. In 28 southern constituencies, no votes will be cast because no candidates could sign up.
The Election Commission says results will not be available on Sunday. Its commissioners are braced for a deluge of complaints and challenges to the results.
"There's been a lot of obstruction, so much, every single step of the way," commission secretary-general Puchong Nutrawong told Reuters.
"We don't want this election to be a bloody election. We can get every single agency involved to make this election happen, but if there's bloodshed, what's the point?"
Anti-government demonstrators say Thaksin subverted Thailand's fragile democracy by entrenching money politics and using taxpayers' money for generous subsidies, cheap healthcare and easy loans that have bought him loyalty from millions of working-class Thai voters in the north and northeast.
With broad support from Bangkok's middle class and tacit backing of the royalist establishment, old-money elite and military, the protesters reject the election and want to suspend democracy, replacing it with an appointed "people's council" to reform politics and erode Thaksin's influence.
The latest round of tumult in the eight-year political conflict erupted in November and underscored Thaksin's central role in the intractable struggle, both as hero and villain.
Yingluck was largely tolerated by Thaksin's opponents but her party miscalculated when it tried to introduce a blanket amnesty that would have nullified a graft conviction against Thaksin and allowed him to return home.
Many Thais see history repeating itself after a cycle of elections, protests and military or judicial interventions that have polarized the country and angered Thaksin's "red shirt" supporters, who held crippling blockades in 2010 and have vowed to defend his sister from any overthrow attempt.
Thailand's military has remained neutral so far, but the judiciary has taken on an unusually large number of cases in the past two months in response to complaints against Yingluck and Puea Thai that could result in the party's dissolution and lengthy bans for its top politicians.
(Read more: Thai protest leader rejects compromise but says no civil war)
There is also a chance the election could be annulled, as it was in 2006, over a technicality. The Election Commission is expecting lawsuits to be filed demanding the election be voided.
The main opposition Democrat Party is boycotting the poll and the commission has already voiced concerns that it would result in too few legitimately elected MPs to form a parliamentary quorum.
With no quorum to re-elect a prime minister, it looks likely Yingluck could be a caretaker premier for months. Even with a fresh mandate, a stalemate is almost certain, giving her opponents more time to intensify their campaign against her and for legal challenges to be lodged.