Here are some of the possible scenarios after the first vote in eight years.
- Junta triumphs -
Thailand's junta stands a good chance of emerging victorious.
Former general Prayut Chan-O-Cha, who took power in 2014, benefits from a junta-crafted charter that tilts the scales in his favour.
It allows the junta to appoint a 250-member Upper House, meaning Prayut's Phalang Pracharat party needs only 126 of the Lower House's 500 MPs to select the premier.
By contrast, its rivals need to win 376 seats in the Lower House to secure a simple parliamentary majority of the 750 seats.
But Prayut's return as a civilian premier may be hamstrung by questions of legitimacy if he is reliant on the unelected Senate.
- Democratic revival -
Anti-junta parties face an uphill battle but they could unite to defy the odds.
The military-scripted charter limits the number of seats large parties -- like Pheu Thai, linked to the political machine of exiled ex-premier Thaksin Shinawatra -- can win.
It is designed to keep "Thaksin-aligned parties from emerging with a large number of MPs", said analyst Thitinan Pongsudhirak of Chulalongkorn University.
Thai Raksa Chart, a Pheu Thai offshoot created to scoop up more votes, was dissolved following its ill-fated bid to have Princess Ubolratana run as its prime ministerial candidate.
But Shinawatra-linked parties have won all elections since 2001, and they are projecting to win 150-200 seats.
Pheu Thai will need to look to other parties to reach the threshold of 376 seats.
The most prominent newcomer is the anti-military Future Forward, whose telegenic billionaire leader Thanathorn Juangroongruangkit has attracted millennial voters.
- 'The Matchmaker' -
More than seven million young Thais are voting for the first time and do not neatly subscribe to traditional political sides.
Their votes and the new system that helps smaller parties win more seats could give "outsider" groups like Future Forward a key role in helping form a government.
Smaller but more established regional parties, like Bhumjaithai, which came third in the last election in 2011, will also be key power brokers.
The party's super-rich leader Anutin Charnvirakul believes they will win the third largest number of seats.
"I will be the matchmaker, but (Thais) will have to decide who to match," he said.
Democrat Party leader Abhisit Vejjajiva -- a former prime minister -- may play a key role too as head of Thailand's second-biggest party in 2011 elections.
But the Democrats have not won a Thai election in almost two decades and they have stated they will not join a Pheu Thai-led coalition at this stage.
-- Deadlock, caretaker government --
With neither side expected to win a comfortable majority, the election could be followed by a prolonged period of horsetrading.
"It will be a mess," political scientist Napisa Waitoolkiat of Naresuan University told AFP.
And with the coronation of King Maha Vajiralongkorn planned just six weeks after the election, the junta "cannot allow any disturbance, any demonstration, any instability during that period."
A caretaker government could be installed by the Election Commission to steer the country peacefully through the coronation, which runs from May 4-6.
But after the coronation is over, she says the question remains: "How long can (the junta) buy time for?"
-- Coup, again? --
The country's coup-peppered history means military power grabs "can never be ruled out," said analyst Thitinan Pongsudhirak, though he called it an "extreme outcome".
If the election were to result in a landslide win for anti-junta parties, "the likelihood of a military option will grow," Thitinan said.
Thailand has seen 12 coups in the last 90 years - an average of one military takeover every seven years.