Nachacha Kongudom had in Thailand been among demonstrators using “three-finger salutes” in demanding the election that was several times delayed before being held in March.
In New York, she managed to get a protest sign into the building where Prayut was speaking and shouted at him before being escorted out by security guards.
Prayut responded to her action by saying, “Hello, thank you, thank you very much.”
Photos shared on social media indicated that other Thais were protesting outside the hall.
Prayut told the audience the military junta he led to power in the 2014 coup sought only to end a bloody political conflict and that the government it established approved 400 laws.
Prayut was in New York primarily to attend a meeting of the UN General Assembly.
aran Ditapichai, president of the Association of Thai Democrats without Borders, wrote to the United Nations on Monday asking that Prayut’s new administration be regarded as “a military government in disguise”.
A billboard mounted on a building close to UN headquarters carried the message “United Nations Assembly: Don’t let democracy die in Thailand”.