Ronald Post, who spent 28 years on death row for the 1983 killing of a hotel worker, had been due to die by lethal injection in January.
But he won a reprieve in December last year after his lawyers filed a motion arguing that a lethal injection would be "torturous and lingering" due to his enormous size.
Post's lawyers had argued that such an injection could take up to 16 hours to work.
"His death was expected," the spokesman told AFP, adding that his health had deteriorated.
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Post's death penalty was commuted to life in prisonment without the possibility of parole after Ohio Governor John Kasich ruled he had not received a good enough defense at his trial.
Kasich did not refer to Post's weight when he announced last December that the prisoner's execution would not go ahead.
"The Parole Board's conclusion is that Ronald Post did not come close to receiving such a defense. After my own careful review, I agree," Kasich said at the time.