Tony A. de Brum, a longtime political leader in the Republic of the Marshall Islands who helped negotiate his country’s independence in the 1970s and decades later fought for its survival in the face of climate change, died on Monday in the capital city, Majuro. He was 72.

Hilda C. Heine, the country’s president, announced his death.

President Heine called Mr. de Brum a “national hero” for advocating for nuclear disarmament and for giving the Marshall Islands, in the central Pacific, an outsize voice in global climate-change negotiations.

In dozens of speeches to the United Nations over the years and in various government roles, Mr. de Brum would weave together the dominant themes of his country: the struggle for independence, the lingering suffering from nuclear testing that the islanders had endured, and the threat of rising sea levels from climate change.