Edward Seaga, a former prime minister of Jamaica who helped set that island nation on a conservative course and forged a close relationship with the United States, died in Miami on Tuesday, his 89th birthday.

His death was announced on Twitter by Andrew Holness, Jamaica’s current prime minister. No other details were given. The Jamaican news media reported that Mr. Seaga (pronounced see-AH-ga) was being treated in Miami for cancer.

Much of Mr. Seaga’s career, as leader of the Jamaica Labor Party and as prime minister, was spent tilting in opposition to his political nemesis, Michael Manley.

In the late 1960s and early ′70s, the leftist People’s National Party was gaining power, with Mr. Manley as its head. He was elected prime minister in 1972. Pushing a populist agenda, Mr. Manley established a minimum wage, built housing projects and fostered closer ties with Cuba, all in sharp contrast to the policies of Mr. Seaga and the Labor Party.