But after an election campaign that has featured a huge and unlikely cast of would be prime ministers - a general, a (quickly disqualified) princess, a 40 year-old-billionaire and the nation's first transgender candidate among them - and despite voters being hungry for change, there is every chance the poll will do little more than affirm the status quo ante of rule by military junta leader Prayut Chan-o-cha.

That won't be because of a lack of interest in the election in this mostly Buddhist nation of about 70 million people.

Rather, the complicated electoral system introduced in 2017's new constitution, which is effectively designed to ensure no big party wins a majority in the lower house, and which allows the military-appointed Senate a big say in choosing the next prime minister, means a minority government led by Prayut is in the offing, as is a renewed period of political uncertainty.

On Friday, the last full day of campaigning, tens of thousands of Thais attended rallies across the capital, Bangkok.

Junta leader Prayut, who is now campaigning to be elected prime minister at the top of the Palang Pracharat Party ticket - but who is doing poorly in polls in much of the country - theatrically declared, "I will die for this land, this land is sacred" during his first "official" appearance of the campaign.

Democrats leader and former prime minister Abhisit Vejjajiva, who is hoping to secure enough seats to emerge as a compromise candidate, roused supporters at a separate rally across town.

Pheu Thai, the party likely to win the highest number of seats and which is aligned with exiled former prime minister Thaksin Shinawatra, urged its supporters to vote for it in a landslide so it can "be the core of the next government".

That seemed to be an acknowledgment that unlike in 2001 and 2011, when parties loyal to Thaksin won general elections before being deposed in coups, this time around Pheu Thai won't be able to govern in its own right.

Next door to the Pheu Thai rally, the Future Forward party, which is led by the charismatic, photogenic and social-media-friendly 40-year-old billionaire Thanathorn Juangroongruangkit, was hailed by thousands of Thais as the face of democratic change.

Thanathorn told the Sydney Morning Herald and The Age he was "very confident" his party would pick up seats across the country, and not just in its base of Bangkok, and set out three key goals.

"The first mission is to stop the continuation of the NCPO [the National Council for Peace and Order military junta] regime. Mission number two is to amend the constitution of 2017 and, number three, it’s about annulling the legacy of the military junta," he said.

"These are the three things we wouldn’t compromise. Other things we can talk. But these three conditions are our principles. Don’t lose your principles when you are talking about forming a government."

A total of 52 million Thais are eligible to vote on Sunday, including an estimated 7.1 million people who will be able to vote for the first time.

Already there are concerns about how impartial the Electoral Commission has been, and allegations of vote buying have surfaced too.

Future Forward is hugely popular with young voters, according to political analysts, and is likely to win between 20 and 30 seats of the 150 proportional representation seats in the lower house. It may also pick up a handful of the 350 constituency seats in the lower house.

Even with Pheu Thai expected to win large swaths of seats in its strongholds in the north and north-east of the country - and even if Future Forward and other opposition parties exceed expectations - it's unlikely the opposition parties will be able to combine to claim the majority of 376 seats needed to select the prime minister in a joint, 750-member sitting of the two houses.

Thitinan Pongsudhirak, a politics professor at Bangkok's Chulalongkorn University, said the most likely result was a "status quo upgrade".

"There will be elections, with some semblance of popular legitimacy. But the realty is the junta regime will likely continue," he said.

Prayut's party is expected to win 60 to 80 seats, Thitinan said, but they "should be doing so much better - they have all the organs of the state at their disposal''.

Prayut and his Palang Pracharat party will therefore fall short of the 126 seats needed in the lower house to install him as prime minister (assuming the handpicked 250 senators all vote for the regime candidate).

That could leave the royalist Democrats playing king maker - though whether that means the Democrats back Prayut to be prime minister or manage to install their own leader, Abhisit, remains to be seen.

That also means a situation could emerge where the governing party is in the minority in the lower house, and the opposition parties holds a majority of seats - opening up the prospect of a censure or even no-confidence vote almost immediately.

Perhaps 90 per cent of the results will be known within hours of the polls closing on Sunday, though the official results won't be declared until May 9.

And with the deck stacked to try to avoid another landslide win for the opposition, the political horse trading over who will emerge as a compromise candidate will be fierce.

Whoever wins out, an unstable coalition government seems likely.