But over the past two decades, some of those who knew and worked with Eastman, especially the composer Mary Jane Leach, have been painstakingly collecting and restoring his scattered works. In 2005, New World Records issued the first commercial Eastman release, a three-disc set called “Unjust Malaise.” In 2015, “Gay Guerrilla,” a book of essays that takes its title from one of his works, was published. This winter, The Kitchen, in New York City, presented “Julius Eastman: That Which is Fundamental,” an ambitious three-week festival.

“Now Julius has become the darling of this whole scene,” his younger brother, Gerry Eastman, a jazz musician responsible for Julius’s estate, said in a telephone interview. “I just wish he’d lived a bit longer.”

Mr. Eastman, 72, said that he was delighted that his brother’s music had been rediscovered, relieved that he would no longer have to serve as the gatekeeper for it, and that he expected the deal to bring the music to a much wider audience. He said that after years of people performing Eastman works for little or no money — and even large festivals haggling for fees he considered exploitatively low — the partnership with Schirmer would ensure the Eastman estate got its due.

“I’m relieved that they are taking this over,” he said. “We made a really good deal for both of us.”