Chi Chia-wei, a pioneering Taiwanese gay rights campaigner whose lawsuit helped lead to the constitutional court ruling, said in an interview before the parade that he was “extremely disappointed” in the government’s lack of movement on same-sex marriage.

“If you make a promise as a politician, you have to follow through on it,” Mr. Chi said. “If you don’t, you’re just playing politics; you’re a liar.”

Ms. Tsai, who as a presidential candidate in 2015 courted the lesbian, gay, bisexual and transgender vote and called for legalizing same-sex marriage, welcomed the court’s ruling in May 2017, saying on Twitter, “The law must protect the people’s freedom of marriage and right to equality.”

But her support since then has seemed more reserved. In a June interview with Agence France-Presse, rather than speaking of rights, she said that Taiwan was divided on the issue, while promising that the government would “bridge the differences” and “propose a comprehensive bill.”