The curfew from 10 pm to 4 am (1500 to 2100 GMT) will begin on Friday, April 3, and bars everyone in the country from leaving their homes.
Exemptions will be made for essential staff, including medical workers, food and fuel transport staff, and postal services.
The number of infections in Thailand has soared past 1,800 – up more than 80% from a week ago – and the death toll has nearly quadrupled to 15 as of Thursday.
The government has come under criticism for not acting soon enough to curb the spread of the virus – introducing incremental measures despite being the first country outside China to confirm a case, which happened in January.
In an address to the nation, Prime Minister Prayut Chan-O-Cha urged citizens not to panic.
"You can buy things in the daytime," he said.
Penalties for hoarding essential supplies such as face masks carry penalties of up to 7 years in prison and a 140,000 baht ($4,200) fine, he said.
The stepped-up measures also include an entry ban on all arrivals – including Thais – for two weeks.
Thais who insist on returning will be placed under state quarantine, though Prayut implored them to defer travel plans.
On Thursday, Bangkok's popular markets were shuttered, while parks that were ordered to close were empty of joggers.
Thailand's economy has been hit hard by the coronavirus, especially those employed in the informal sector.
The Bank of Thailand expects the economy to shrink by 5.3% this year – a 22-year low – and nearly 22 million people have registered for cash handouts. – Rappler.com