Midfielder Elise Bussaglia opened the scoring on the hour mark from a short corner routine that Thailand failed to clear.
Substitute Kadidiatou Diani then scored twice in eight minutes to seal the win, capitalising on a mix-up to score her first goal before pouncing on a rebound from Chor Charoenying's penalty save off Eve Perisset to grab her second in the 86th minute.
France play one more warm-up game, against China on Friday, before kicking off their World Cup campaign on June 7 against South Korea. Thailand, who have qualified for their second World Cup, play defending champions United States on June 11.
(Reporting by Rohith Nair in Bengaluru; editing by Clare Fallon)