The Boston-based organization said Farmer “unexpectedly passed away today in his sleep while in Rwanda,” where he had been teaching.

Farmer was a professor of medicine at Harvard Medical School and chief of the division of global health equity at Brigham and Women’s Hospital. He wrote extensively on health, human rights and social inequality, according to Partners in Health.

“Paul Farmer’s loss is devastating, but his vision for the world will live on through Partners in Health. Paul taught all those around him the power of accompaniment, love for one another, and solidarity,” Partners in Health CEO Dr. Sheila Davis said in a written statement.

Partners in Health, founded in 1987, said its mission is “to provide a preferential option for the poor in health care.”

“By establishing long-term relationships with sister organizations based in settings of poverty, Partners in Health strives to achieve two overarching goals: to bring the benefits of modern medical science to those most in need of them and to serve as an antidote to despair,” the organization said on its website.

The organization works in a number of areas including Africa, Eastern Europe and Latin America. Farmer also worked to build health systems in Haiti.

Michelle Karshan, vice president of a nonprofit prison health care system in Haiti who worked closely with Farmer, said he was determined, innovative and always knew how to get around obstacles and bureaucracy.

“He didn’t take no for an answer,” she said. “He didn’t think anybody was too poor or too illiterate to be entitled to receive health care.”

She noted that when the World Health Organization resisted giving HIV medication to people who were illiterate in Haiti for fear they would not know when or how to take it, Farmer set up his own program and created a chart that relied on the sun’s position. He also hired people known as “accompaniers,” who would hike through Haiti’s rough mountainous terrain to make sure patients had water, food and were taking their medications.

“I’m so sad for all the people who are not going to have him in their lives. He was there for everybody,” Karshan said.

Former President Bill Clinton praised Farmer’s work.

“Paul Farmer changed the way health care is delivered in the most impoverished places on Earth. He saw every day as a new opportunity to teach, learn, give, and serve — and it was impossible to spend any time with him and not feel the same,” Clinton said in a statement.

At the beginning of the COVID-19 pandemic, with thousands of cases reported daily in Massachusetts, local health departments were overwhelmed by the task of contact tracing to help slow the spread of the disease.

The state launched a contact tracing collaborative in April 2020, and asked Partners in Health to lead the initiative, which made more than 2.7 million calls to residents at a total cost of about $158 million, according to the state.

Farmer is survived by his wife, Didi Bertrand Farmer, and their three children.