Vaccinated tourists from more than 60 “low-risk” nations are allowed to enter the country and avoid hotel quarantine.
Tourist numbers are forecast to jump to as much as 15 million next year, bringing in more than $30bn (£22bn).
However, much of country still faces restrictions, with only around 42% of the population fully-vaccinated.
Thailand is still registering almost 10,000 Covid infections a day.
“It’s like seeing a very dim light at the end of the tunnel – we haven’t been able to work in two years,” tour guide Chaiyagorn Boonyapak told BBC. But he and his fellow tour guides haven’t been contacted by customers and tour companies yet and it could take a month until tours are back up and running again.
The coronavirus pandemic hammered Thailand’s economy, which would previously attract 40m tourists a year. Last year, tourist arrivals were down more than 80%.
Airports serving Bangkok and Phuket are among those opening to countries including UK, China, Japan, the US and most of Europe.
The Thai government predicts revenues to rebound to their pre-pandemic levels by 2023, although many industry experts say China’s ongoing border closures will hamper the sector’s recovery.
Before the pandemic, Chinese tourists made up the biggest number of tourists, with some 12m visitors arriving from China in 2019.