McCarthy died in his sleep at assisted living home in the Georgetown neighborhood where he had lived for the past few years, said his son, Michael.
Eugene McCarthy challenged President Lyndon B. Johnson for the 1968 Democratic nomination during growing debate over the Vietnam War. The challenge led to Johnson's withdrawal from the race.
The former college professor, who ran for president five times in all, was in some ways an atypical politician, a man with a witty, erudite speaking style who wrote poetry in his spare time and was the author of several books.
"He was thoughtful and he was principled and he was compassionate and he had a good sense of humor," his son said.
When Eugene McCarthy ran for president in 1992, he explained his decision to leave the seclusion of his home in rural Woodville, Va., for the campaign trail by quoting Plutarch, the ancient Greek historian: "They are wrong who think that politics is like an ocean voyage or military campaign, something to be done with some particular end in view."
McCarthy got less than 1 percent of the vote in 1992 in New Hampshire, the state where he helped change history 24 years earlier.
Helped by his legion of idealistic young volunteers known as "clean-for-Gene kids," McCarthy got 42 percent of the vote in the state's 1968 Democratic primary. That showing embarrassed Johnson into withdrawing from the race and throwing his support to his vice president, Hubert H. Humphrey.
Sen. Robert Kennedy of New York also decided to seek the nomination, but was assassinated in June 1968. McCarthy and his followers went to the party convention in Chicago, where fellow Minnesotan Humphrey won the nomination amid bitter strife both on the convention floor and in the streets.
He was a firecracker.