It now owns 75% of the company.
ThaiBev bought a 75% stake in Myanmar Supply Chain (MSC) and Myanmar Distillery (MDC) for US$742m.
According to RHB, the MSC and MDC operate two spirit production facilities in Yangon and Mandalay under the Grand Royal brand, which currently dominates Myanmar's whisky market with a 70% market share.
The acquisition marks ThaiBev's comeback in Myanmar's alcohol market, after Fraser & Neave (F&N) sold its stake in the Myanmar Brewery in 2015.
Myanmar's per capita consumption of spirit is still "very low" compared to other non-Muslim countries in Asia. Volume of spirit consumption could grow by as much as 9% within the next five years.
"We believe the acquisition would also give ThaiBev a strong distribution network to export its portfolio of alcohol products to the emerging markets," said RHB analyst Juliana Cai.