When he was 26, Joe McGinniss wrote "The Selling of the President 1968," a landmark study of the uses of advertising in presidential campaigns. It stayed on bestseller lists for seven months, making Mr. McGinniss the youngest living author, up to that point, to have a No. 1 nonfiction bestseller.
At 40, he published "Fatal Vision," a page-turning tale about Jeffrey MacDonald, an Army doctor who continued to maintain his innocence long after he was convicted of murdering his wife and two daughters.
"Fatal Vision" sold millions of copies, was made into an NBC miniseries and was hailed as a true-crime classic. But in later years, the book became the centerpiece of an impassioned debate about journalistic ethics, which came to overshadow Mr. McGinniss' early reputation as one of the leading nonfiction authors of his generation.
Mr. McGinniss was 71 when he died March 10 at a hospital in Worcester, Mass. The cause was prostate cancer, his wife, Nancy Doherty, said.
He was still writing until shortly before his death, chronicling his struggle with cancer in Facebook updates and in an unfinished book, but in many ways he became better known for what people said about him than for what he actually put on the page.
In 1968, while a columnist for The Philadelphia Inquirer, Mr. McGinniss overheard an advertising executive say that his company had acquired the "Humphrey account." Until that moment, Mr. McGinniss had not realized that presidential campaigns hired teams of advertisers to sell their candidates like a brand of soap.
When Democratic candidate Hubert Humphrey's handlers turned down Mr. McGinniss' request to peek behind the scenes, he approached the Republican candidate, Richard Nixon. Nixon's people agreed to let him into the inner sanctum.
"The Selling of the President 1968" became a runaway bestseller when it was published in 1969 and was later made into a Broadway play.
The book irreverently pulled back the curtain on political marketing and heralded a promising career for its author, the youngest writer other than Anne Frank to top the nonfiction list up to that point.
Mr. McGinniss published two books in the 1970s, then journeyed to Alaska for "Going to Extremes," his 1980 account of the dark side of the Alaskan dream.
In the late 1970s, Mr. McGinniss met MacDonald, a onetime Army doctor whose pregnant wife and daughter had been bludgeoned and stabbed to death in 1970 at their home in North Carolina.
They began on friendly terms, and Mr. McGinniss agreed to share up to a third of the profits from a book about MacDonald. The doctor said his family had been attacked in the middle of the night by a Charles Manson-like group of hippies, chanting "Acid is groovy."
But MacDonald was convicted of murder in 1979, and Mr. McGinniss came to believe he was a manipulative psychopath.
MacDonald sued Mr. McGinniss for $15 million, saying he had been betrayed by the author, and the case was ultimately settled out of court, with Mr. McGinniss' publishers paying MacDonald $325,000, in return for MacDonald's agreement that Mr. McGinniss had done nothing legally wrong.
Joseph McGinniss was born Dec. 9, 1942, in New York City, where his father ran a travel agency.
According to Mr. McGinniss' wife, his parents allowed him to choose his middle name when was a child. He selected Ralph, after his favorite baseball player, Ralph Kiner, the onetime Pittsburgh Pirates slugger who died Feb. 6.
Mr. McGinniss was a 1964 graduate of the College of the Holy Cross in Worcester, Mass., and worked at newspapers in Port Chester, N.Y., and Worcester before going to Philadelphia. In later years, he lived in Pelham, Mass.