Robert S. Boyd, a journalist who shared a Pulitzer Prize for uncovering evidence that Senator Thomas F. Eagleton had undergone electroshock therapy for depression, a revelation that compelled Senator George S. McGovern to jettison Mr. Eagleton as his Democratic running mate for vice president in 1972, died on Friday in Philadelphia . He was 91 .

The cause was congestive heart failure, his son Tim Boyd said.

The scoop, by Mr. Boyd and a colleague at the Knight Ridder newspaper chain , Clark Hoyt, was based on a tip from a McGovern supporter, a friend of a doctor who had treated Mr. Eagleton and who feared his medical history would be leaked closer to the election, when the revelation might be even more damaging.

“The available evidence at the time indicated that, under stress, he was prone to incapacitating depression,” Mr. Hoyt, who was later the public editor of The New York Times, said of Mr. Eagleton by email. “Can you imagine a president facing an international crisis suddenly unable to function?”

Mr. Hoyt and Mr. Boyd flew to South Dakota, Mr. McGovern’s home state, to present McGovern campaign officials with a two-page memo detailing the reporters’ findings and to give the campaign a chance to respond.