CLEVELAND — Peter Thiel, the Silicon Valley entrepreneur, declared “I am proud to be gay” in a speech on Thursday night, making him the first person believed to utter those words from the stage of a Republican National Convention.

Mr. Thiel’s remarks came about an hour before Mr. Trump spoke, one of the most coveted slots of the week. And he helped cap a convention that began with Republicans’ ratifying what supporters and opponents alike described as their most socially conservative platform ever.

Mr. Thiel is a libertarian who has been drawn to Mr. Trump by a shared belief that America is involved in too many interventions overseas, but his involvement in Republican politics and his embrace of Mr. Trump has made him something of an outlier in Silicon Valley.

His sexuality, and his willingness to embrace it publicly in front of such a large audience, makes him even more of an outlier for a Republican convention.