Seven million millennials are eligible to vote for the first time. Voter turnout is expected to be high among a public weary of junta rule.
Polls in Thai election opened on Sunday. This is the first time the country is going to general elections since the 2014 coup. Polls opened "at 92,320 polling stations across the country," Election Commission secretary-general Jarungvich Phumma told AFP.
Just hours before the opening of polls, Thailand's king Maha Vajiralongkorn issued a statement late Saturday, quoting his late father, and urging the people of Thailand to support "good" leaders to prevent "chaos", news agency AFP reported.
Vajiralongkorn urged the public to "remember and be aware" of the remarks of his father, who died in 2016.
"His majesty is concerned about the stability of the nation, the feelings and happiness of the people," the statement added.
Just a few months ago, Thailand's political scenario heated after another royal command torpedoed the candidacy of his elder sister Princess Ubolratana for prime minister of a party linked to billionaire ex-premier Thaksin Shinawatra.
The move was described by the King as "highly inappropriate".
The party was later dissolved by a court, a fresh chapter of intrigue in the politically combustible country.
Thailand is a constitutional monarchy. But the palace holds unassailable powers and is shielded from criticism by a harsh royal defamation law.
The turbulent kingdom remains bitterly divided despite the junta's pledge to rescue the country from a decade-long treadmill of political instability, protests and coups.
Sunday's election pits a royalist junta and its allies against the Shinawatras' polished electoral machine and an unpredictable wave of millennial voters, whose political loyalties are unknown.
The junta-party, which is proposing army chief turned premier Prayut Chan-O-Cha for civilian prime minister after the polls, is under intense pressure to avoid humiliation on Sunday in what is effectively a referendum on its popularity.
Prayut toppled the civilian government of Thaksin's younger sister Yingluck in 2014.
The army and its allies in the Bangkok elite loathe the Shinawatras, accusing the clan of toxifying Thai politics and society with money, nepotism and graft.
The Shinawatras say they have simply recognised the economic and democratic aspirations of the majority of Thais, reflected in their landslide election wins.
This time the ruling junta has written new election rules aimed at curbing the number of seats big parties -- specifically the Shinawatras' main election vehicle Pheu Thai -- can win.
Pheu Thai is expected to again sweep up the north and northeastern heartlands as it seeks to head an anti-junta coalition.
A 250-member junta-appointed senate and a new proportional system were meant to have manoeuvered Prayut and the junta party -- Phalang Pracharat -- into pole position.
With senate votes in hand, the party needs just 126 lower house seats to secure a parliamentary majority. It can cross that line comfortably with alliances with smaller parties.
Pheu Thai, however, needs 376 lower house seats to command an overall majority -- near impossible without complex tie-ups across pro-democracy factions.
"A deadlock is very likely," political scientist Napisa Waitoolkiat of Naresuan University told AFP.
New demographic forces have complicated the normal split between pro-and anti-Shinawatra factions.
Seven million millennials are eligible to vote for the first time.
Voter turnout is expected to be high among a public weary of junta rule.