“I think it’s been an evolution,” said Judge Kozinski, who served with then-Judge Kennedy on the appeals court. “Maybe what happened is the world around him changed, and the evolution has not been so much in his own thinking, as in the world we live in.”

Justice Kennedy now has a gay clerk, Joshua Matz, who wrote a 2012 law review article with Mr. Tribe titled “The Constitutional Inevitability of Same-Sex Marriage.” A former clerk, Paul T. Cappuccio, who was not openly gay when he worked for the justice in the late 1980s, recently married. When Mr. Cappuccio and his husband became fathers in 2013, Justice Kennedy sent his customary baby gift for clerks: an inscribed pocket Constitution.

And at the McGeorge School of Law campus in Sacramento — where Justice Kennedy taught part time for 23 years and formed a deep intellectual bond with Mr. Schaber as they built the little-known school into a respected institution — an openly gay colleague, Larry Levine, says the justice has helped him get tickets to oral arguments in gay rights cases before the Supreme Court. After each landmark ruling, Mr. Levine said, he has written to Justice Kennedy to say, “both professionally and personally, how meaningful this is.”