"I want to see Thailand become more democratic and inequality eased from society," said insurance company employee Pattrapong Waschiyapong at a Bangkok voting station.
Thailand is a constitutional monarchy and the royal family is nominally above politics. However a palace communiqué issued on the eve of the vote urged voters to make the right choice.
The statement referred to comments made in 1969 by the former monarch Bhumibol Adulyadej. He called on voters to support good people to govern the society and control the bad people.
His son, King Maha Vajiralongkorn, urged the public to remember and be aware of the remarks of his father, who died in 2016.
TV stations throughout the country repeated the statements.
A royal command in February ended the candidacy of the king's elder sister Princess Ubolratana for prime minister of a party linked to Thaksin.
Thaksin has lived in self-exile since 2008 but he looms large over the election. His affiliated parties have won every Thai election since 2001, drawing on loyalty from rural and urban poor.
In Bangkok, Sudarat Keyuraphan, the prime ministerial candidate for the largest Thaksin-linked party Pheu Thai, said he noted the euphoria at the ballot box.
The junta party, which is proposing army-chief-turned premier Prayut Chan-O-Cha for civilian prime minister, is attemping to maintain its hold on power. Prayut toppled the civilian government of Thaksin's younger sister, Yingluck, in 2014.
For the 2019 election, the junta has written election rules aimed at curbing the number of seats big parties - specifically Pheu Thai - can win.
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 in alliance with smaller parties.
However Pheu Thai needs 376 lower house seats to command an overall majority.