Major parties, including Pheu Thai, the Move Forward Party (MFP), United Thai Nation (UTN) Party, Democrat Party, Palang Pracharath Party (PPRP) and Bhumjaithai Party will compete, reported Anadolu.
Thais are politically divided into two poles: those who support military order and those who support civil liberties.
Prayuth Chan-Ocha, a retired Royal Thai Army officer, came to power through a military coup in May 2014, ousting the democratically-elected government of Prime Minister Yingluck Shinawatra.
Chan-Ocha became prime minister of a civilian government, but that government was made up of elected deputies. He has been serving as Thailand's prime minister since 2019.
Opposition Pheu Thai Party, one of the most popular political parties that won five general elections before being ousted by the coup is leading in most polls with a solid support base in rural areas and working-class voters.
The Progressive Movement party is also garnering votes from young voters and democracy advocates after the pro-democracy protests in 2020.
Around 6,679 candidates are contesting for 500 seats in parliament while 63, including nine women, are nominated by 43 parties for the prime ministership, according to Thai PBS World.
Voting will end at 5 pm with preliminary results scheduled to be announced later Sunday.