Ady Barkan, a well-known activist who campaigned for Medicare for all while struggling with the terminal neurodegenerative disease A.L.S., has died. He was 39.

His death was announced on Wednesday by Be a Hero, a political organization that he co-founded in 2018. Mr. Barkan died of complications of A.L.S. at about 6 p.m. local time at Santa Barbara Cottage Hospital in Santa Barbara, Calif, the group said.

Mr. Barkan was diagnosed with A.L.S., or amyotrophic lateral sclerosis, in 2016, four months after the birth of his son, Carl. The disease, which causes paralysis, strikes many patients in the prime of life and often leads to death within two to five years.

As Mr. Barkan confronted his mortality, he dedicated the rest of his life to changing the American health care system.