Early-bird protesters gathered at the intersection before dawn for a candlelight ceremony.
Som, a 16-year-old student protester, said she wasn't worried about the coronavirus risk.
"We have never had any real democracy," she told AFP. "The country is not going anywhere."
Student leader Parit ‘Penguin’ Chiwarak -- who is facing royal defamation charges and was released on bail last month–marched to a drum beat wearing a plastic golden crown and carrying a flag.
Some demonstrators carried signs that read "Abolish 112", a reference to the kingdom's harsh royal defamation laws that carry a 15-year jail term for those convicted of insulting the monarchy.
One protester was dressed like the Statue of Liberty and demonstrators burned a mock constitution–in the same week the Thai parliament debated changes to the country's charter.
"Our demands won't be lowered... The constitution must come from the people," Jatupat "Pai" Boonpattararaksa said over a loudspeaker.
Protesters arrived at the parliament by the afternoon after a prolonged, circuitous march due to a police presence hindering a more direct route.
Outside the legislature opposition MPs received their demands, and a lawmaker from the ruling Phalang Pracharat party, Sira Jenjaka, made a brief appearance on a makeshift stage with the protest leaders.
"We are willing to listen," he said, to loud jeers from the crowd.
The administration of Prayut has increasingly come under fire due to its handling of the pandemic.
"Even those who were on the government's side are now calling out the government's work and criticising failed government efforts," said prominent protest leader Panupong Jadnok as he walked alongside protesters.
The Thai pro-democracy movement sent shockwaves through the country's establishment last year, particularly the most controversial demand–a call to reform how the monarchy operates.
About 150 people have been charged since the movement started, with key leaders hit with multiple counts under Thailand's tough royal defamation laws.
Many of them were released on bail under conditions that include not protesting.
The kingdom has recorded more than 232,600 Covid cases to date and 1,775 deaths.