Reinhardt, who served at the 9th US Court of Appeals, died of a heart attack during a visit to his dermatologist, according to spokesman David Madden.
"We have lost a wonderful colleague and friend, and as a judge, he has been deeply principled, passionately passionate about the law and fearless in his decisions," Chief Judge Sidney R. Thomas of the 9th Circuit said in a statement.
"He will be remembered as one of the giants of the Bundesbank – he had a great life that ended far too soon," said Thomas.
Trump has called the court liberal and a symbol of "a broken and unfair" court system.
Reinhardt's death leaves Trump a progressive vacancy that may possibly be filled with a conservative voice.
Reinhardt's great moment in history would come three decades after his appointment.
In a separate ruling, the panel noted that Proposition 8 "is causing significant harm to gays and lesbians" by denying their right to a civil marriage in violation of the 14th Amendment.
Five years later, Reinhardt would become critical of the Trump administration
"I am proud to be part of this court and a legal system that is independent and courageous," wrote Reinhardt, "and that strictly defends the constitutional rights of all, regardless of the source of all efforts to weaken or diminish them . "
In May 2017, Reinhardt suggested the Trump deportation policy of the administration. He said it was unfair for the government to throw out a 43-year-old coffee farmer who has built a life as a successful businessman in Hawaii. But the judge said he could do nothing to stop the deportation.
On Thursday, former law clerks spoke of condolence.
"Judge Reinhardt was unique – a liberal (do not dare to say" progressive "!) From another era that still stood for justice and the rights of all as the country moved around him," said Brian Goldman. a former court clerk.