The extension, to take effect from October, is part of the government's efforts to boost economic recovery post-pandemic as it eyes 8-10 million foreign arrivals this year, Bangkok Post reported.
Thailand, one of the world's most popular travel destinations, has lifted all Covid restrictions for foreign tourists and seen 3.78 million tourists arrive this year.
Vietnam reopened its borders in mid-March and resumed its visa exemption policy for 24 countries with maximum stays of 15-30 days.