MONTPELIER, Vt.—A man who renounced his U.S. citizenship in 1948 and for the next six decades led a movement for global citizenship has died in Vermont, his organization said.

The World Service Authority, the administrative wing of the World Government of World Citizens, confirmed that founder Garry Davis died Wednesday in Williston. He was 91.

The group’s main goal is “creating institutions of law at the global level that will allow every human being to live together peacefully,” David Gallup, president and general counsel of the Washington-based World Service Authority, said in an interview Monday.

Davis’ work stretched from his dramatic declaration of world citizenship in Paris in 1948 to his organization’s recent granting of a “world passport” to former National Security Agency contractor Edward Snowden.

His activism was born of grief over his brother’s death in World War II and guilt over his own role as a bomber pilot.

Davis wrote that he thought as he flew bombing missions over Brandenburg, Germany, that he was avenging the death of his brother, who died in the Allied invasion of Italy.

“But it didn’t help,” he wrote. “Because I couldn’t forget those civilians who died under my bombs.”

The war traumatized Davis, his son, Troy, said in an interview. The younger Davis, a lecturer in political science at universities in Strasbourg, France, and Freiburg, Germany, added that his father “sublimated his trauma into trying to figure out, how can this system end?”

Mid-20th-century luminaries including Einstein and Camus spoke out or wrote at various times in support of a global government being the key to ending wars between nations. Davis sought to turn the theoretical into the practical, with his group issuing passports and other documents declaring their bearers global citizens.

Davis said his father determined that the mutual good will most humans share was not enough; political structures—a world government—must be put in place, he believed. Troy Davis pointed to the success of the European Union in keeping the peace for half a century on a continent riven by war for 2,000 years before that.

But the documents were recognized in just a handful of small countries, and the fees that Davis’ group charged for them drew fire from critics, The New York Times reported.

Gallup said Davis had battled cancer but had remained active until days before his death. “He was driving his car last week. The previous Sunday he had done his radio show,” Gallup said.

“I feel so privileged and honored to have worked with Garry Davis for many years and to have had him as my mentor,” Gallup said.

Davis was born Sol Gareth Davis in 1921 in Bar Harbor, Maine. His parents were the former Hilda Emery and Meyer Davis, a well-known bandleader of the time. Davis, too, gravitated toward music. Though he got a degree from the Carnegie Institute of Technology in Pittsburgh, he later worked on Broadway, acting and singing in several shows.