David Joseph Miljoner, a social-justice activist, who grew up in Brooklyn and Oceanside, and later moved to Seattle to work for the U.S. Labor Department, has died. He was 34.

The 2000 Oceanside High School graduate on Saturday died from lymphoma, an illness that was complicated by lupus, said his father, Irv Miljoner, who heads the Long Island office of the U.S. Labor Department.

David Miljoner obtained an undergraduate degree in English and economics and a master’s in political economy and Latin American affairs from the University at Albany, a SUNY school. While there, he was involved in worker and immigrant-rights issues, his father said.

His studies took him to South America, where he traveled extensively, and he worked as a graduate-student fellow in the Peruvian Congress.

“David was not only smart and committed to the cause of social justice, he was adventuresome, insightful, generous and caring, and the most courageous person I’ve ever known,” his father said. “David was the better part of me, and he was loved by everyone who knew him. ”

The younger Miljoner eventually followed in his father’s footsteps, and in 2007 joined the U.S. Department of Labor’s office in Seattle as an investigator.

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He moved to the department’s San Francisco regional office in 2012 and later returned to the Seattle office as an assistant district director.

“He resolved numerous cases on behalf of vulnerable, low-wage and exploited workers,” his father said.

In addition to his father, he is survived by his husband, Sean Dougherty; his mother, Mary Ellen Byers, and his stepfather, Tom Byers, both of Wantagh; his sister, Lisa Miljoner of Freeport; and his stepmother, Shari Miljoner of Oceanside.

The funeral will take place Tuesday, in Seattle. A Long Island memorial service will take place at a later date.