Bui Tin, a North Vietnamese colonel who had a prominent role in the Vietnam War’s final moments but later fled the country and became an unlikely critic of its ruling Communist Party, died on Saturday in France. He was 90.

His death, in the Parisian suburb Montreuil, went unacknowledged by Vietnam’s state-run news media but was confirmed on Monday by his longtime friend Nguyen Van Huy, a fellow Vietnamese dissident who lives in France.

Mr. Huy said in a telephone interview that the exact cause of death was unknown but that Colonel Tin had been in a coma and had received kidney dialysis.

Colonel Tin personally accepted the surrender of South Vietnam in 1975. He was also present at the battle of Dien Bien Phu in 1954, when Vietnamese revolutionaries defeated French troops to secure their country’s independence.