About 500 people marched around Manila's Rizal Park, many carrying placards and streamers saying "Fight for Love" and waving rainbow banners. Some came with pets dressed in rainbow costumes.
Jonas Bagas, executive director of the pro-LGBT rights group TLF Share, said the US court ruling "will reverberate in other corners of the world."
The rally was scheduled to commemorate the 1969 demonstrations in New York City that started the gay rights movement around the world. Bagas said the US court's decision yesterday made it more significant.
"We hope that after this decision, the struggle for equality can be reframed to go beyond marriage equality so that we can address other dehumanising situations that LGBTs encounter," he said.
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Sylvia Estrada Claudio, a gender rights advocate and professor of women development studies at the University of the Philippines, said the decision was also "a triumph for feminism" because of the "intimate connections" between discrimination based on biological gender and discrimination based on sexual orientation, gender identity and expression.
Same-sex unions are not legally recognised in the Philippines because the country's civil code limits marriages to a man and a woman.