McCarthy died of natural causes at Cape Cod Hospital in Hyannis, Mass., said his daughter Lillah.
New York in the late 1930s, McCarthy played Biff Loman opposite Paul Muni's Willy in the 1949 London production of "Death of a Salesman."
Reprising his role in the 1951 film version opposite Fredric March, he earned a supporting-actor Oscar nomination and won a Golden Globe as most promising male newcomer.
McCarthy had appeared in several other films and had a string of TV anthology-series credits behind him when he was cast as Dr. Miles Bennell in "Invasion of the Body Snatchers," director Don Siegel's thriller about an unsuspecting California town whose residents were being replaced by emotionless alien clones grown in oversized seed pods.
In the film's most memorable scene, McCarthy's frantic Bennell runs into traffic, screaming to motorists, "Stop and listen to me! …. They're not human! … Can't you see? Everyone! They're here already. You're next!"
The low-budget film became an enduring cult classic that was selected for preservation in the Library of Congress' National Film Registry in 1994.
McCarthy, who made a cameo appearance in the 1978 remake, got a lot of mileage out of the original film in his later years, appearing often as a guest at film festivals and autograph shows.
"I must say I'm enthralled by the power of the picture all over the world," he told the Knoxville News-Sentinel in 2000. "It's the science-fiction picture of our time. The toasts just keep coming my way."
McCarthy dismissed assertions that "Invasion of the Body Snatchers" was an allegory about the communist infiltration of America or an indictment of McCarthyism.
"There was no assignment of political points of view when we were making the film," he told the Bangor Daily News in 1997. "People began to think of McCarthyism later.
"I thought it was really about the onset of a kind of life where the corporate people are trying to tell you how to live, what to do, how to behave. And you become puppets to these merchants that are somehow turning individuals into victims.
"It seemed to me to be about conforming, the need to control life so it would be more tolerable."
McCarthy's long career included numerous guest appearances on TV series including "The Twilight Zone," "Burke's Law," "Flamingo Road" and "Murder, She Wrote."
He appeared in about 50 films, including "An Annapolis Story," "40 Pounds of Trouble," "The Prize," "The Best Man," "Kansas City Bomber," "Buffalo Bill and the Indians," "Piranha" and "The Howling."
In addition to his many Broadway and other stage credits, McCarthy toured for many years as President Truman in the one-man show "Give 'Em Hell, Harry."
He also was a footnote in the movie career of Marilyn Monroe, playing the husband Monroe divorced in Reno at the outset of "The Misfits," the Arthur Miller-written, John Huston-directed 1961 drama starring Monroe, Clark Gable and Montgomery Clift.
McCarthy had to be talked into playing the role, in which he and Monroe talk on the courthouse steps.
"They wanted me to come out for it, but I was too vain," he told the Columbus Dispatch in 2003. "I said the part was too small. I finally said I would do it if they paid me a hundred dollars a word. They said they would. Turns out I had 29 words."
The son of a lawyer and his homemaker wife, McCarthy was born Feb. 15, 1914, in Seattle. He and his two brothers and sister — Mary McCarthy, who later became an author and wrote the bestselling novel "The Group" — were orphaned when both parents died in the 1918 flu epidemic, and were sent to live with relatives.
McCarthy began acting in the 1930s at the University of Minnesota, where, on a dare from a friend, he played a bit part in "Henry IV, Part 1."
"That day, I realized that I could do something," he told the Bangor Daily News. "I didn't study acting. I didn't even think about it. But evidently I have some innate ability, some talent. It was maybe a gift. In any case, I was in one play after another after that."
After moving to New York, he made his Broadway debut in 1938 in a small role in " Abe Lincoln in Illinois," starring Raymond Massey. As Sgt. Kevin McCarthy during World War II, he appeared in Moss Hart's "Winged Victory," the Broadway play produced by the Army Air Forces.
McCarthy appeared in several Broadway plays in the years immediately after the war, including Maxwell Anderson's short-lived "Truckline Cafe" with Marlon Brando and Karl Malden. He was a founding member of the Actors Studio.
In addition to his daughter, he is survived by his wife of 31 years, Kate Crane McCarthy; children James Kevin McCarthy, Mary Dabney McCarthy, Tess McCarthy and Patrick McCarthy; stepdaughter Kara Lichtman; a brother, Preston; and three grandchildren. He was divorced from actress Augusta Dabney, who died in 2008.