The cause of death was not immediately known.
Peck was nominated for five Academy Awards, winning the Best Actor Oscar for his 1962 performance as the small town Southern lawyer Atticus Finch in the movie adaptation of Harper Lee's Pulitzer Prize-winning novel "To Kill a Mockingbird."
Finch was named just last week as the top movie hero of all time in a poll of experts conducted by the American Film Institute.
The handsome, lanky, dark-haired Peck began performing professionally on the New York stage before turning to film in the early 1940s. With his rugged good looks and resonant voice, Peck was a star within a year after arriving in Hollywood -- usually playing men of particular moral fiber, often characters who reflected his own liberal political views.
A shoulder and spine injury he incurred while a oarsman on a college racing team kept him out of the service in World War II, and may have contributed to his early success in movies. Peck was able to develop a following while other leading men of the day, such as Clark Gable, were in the service and had to re-establish their acting careers on their return.
Between 1945 and 1949, Peck was nominated for the Best Actor Oscar four times -- for "The Keys of the Kingdom" (1945), "The Yearling" (1946), "Gentleman's Agreement" (1947) and "Twelve O'Clock High" (1949).
In later years he starred in such box-office hits as "The Omen" (1976) and "The Boys From Brazil" (1978).
Peck was one of the first Hollywood stars to operate independently of the studio system. He turned to producing with the 1958 Western "The Big Country."
In 1971, he produced the political drama "The Trial of the Catonsville Nine," about a raid by antiwar activists on a Selective Service office in Maryland during the Vietnam War. The film was not widely distributed, but it earned Peck a place on the Nixon White House "enemies list," disclosed during the Watergate hearings in the 1970s.
In 1987, Peck took a role that drew a brickbat from former fellow actor Ronald Reagan. While the Senate was holding confirmation hearings on Reagan's nomination of Judge Robert Bork to the Supreme Court, Peck used his authoritative voice to narrate a TV ad, sponsored by the liberal public interest group People for the American Way, opposing the conservative judge.
Asked what he thought of Peck's performance in the ad, Reagan said, "He's miscast."
Reagan spokesman Marlin Fitzwater said Peck "ought to be ashamed" for the anti-Bork ad.
Peck received most of the major awards Hollywood has to offer.
He received the Screen Actors Guild Lifetime Achievement Award in 1970. In 1968, the Hollywood Foreign Press Association presented Peck with its top honor, the Cecil B. DeMille Award. The Academy of Motion Picture Arts & Sciences honored Peck in 1967 with its Jean Hersholt Humanitarian Award.
The American Film Institute honored Peck with its Lifetime Achievement Award in 1989, and Peck was presented with the Kennedy Center Honors in 1991. He was named a member of France's Legion of Honor in 1993.
In 1999, Peck received a sustained standing ovation when he was announced as winner of the Golden Globe Award for best supporting actor in a mini-series or motion picture made for TV, for his performance as Father Mapple in "Moby Dick." It was to be his last film role.
Later that year, Peck was ranked No. 12 on the AFI list of the greatest American male screen legends.
He remained in good health well into his 70s. In December 1994, Peck was hospitalized overnight in Los Angeles with stomach problems. A battery of tests found the ailment was nothing more than a flu bug.
Peck was married twice. His first wife, the former Greta Konen, was the mother of his three sons -- Jonathan, Stephen and Carey Paul. The couple divorced in 1955. Jonathan Peck, a TV broadcaster, committed suicide in 1975.
Peck had been married since 1955 to Veronique Passani, a French journalist with whom he had two more children, Anthony and Cecilia.
Peck, who once planned a career as a doctor, was born Eldred Gregory Peck in La Jolla, Calif., on April 5, 1916, the son of a pharmacist. At the University of California, he changed his major from premed to English literature when he became interested in the theater.
After his graduation in 1939, Peck headed for New York City and an acting career. He held several other positions first, however, starting as a barker at the Meteor Speedway and then working as a tour guide at Radio City.
While at Radio City, he won a two-year scholarship to the New York Neighborhood Playhouse School of Dramatics, and in the summer of 1940 he won the Barter Theater Award, annually endowed by actress Dorothy Stickney. The award permitted Peck to appear in seven plays in 10 weeks at the famous Barter Theater in Abingdon, Va.
Manager Guthrie McClintic saw Peck in his final play at the playhouse in 1941 and signed him to tour with Katherine Cornell in "The Doctor's Dilemma."
Thereafter, he appeared on Broadway in unsuccessful productions of "The Morning Star," "The Willow and I" and "Sons and Soldiers." Though the plays were flops, the 6-foot-2-inch Peck received good notices. It was then that Hollywood became interested, and Casey Robinson signed Peck for a starring role in "Days of Glory" for RKO in 1943.
In 1995 Peck announced he was retiring from the movie business. He became a hit on the lecture tour, and his live talks formed the basis for Barbara Kopple's 1999 documentary "A Conversation with Gregory Peck."
Among Peck's major films: "Duel in the Sun" (1946); "The Gunfighter" (1950); "David and Bathsheba" and "Captain Horatio Hornblower" (1951); "Only the Valiant" and "The Snows of Kilimanjaro" (1952); "Roman Holiday" (1953); "The Man in the Gray Flannel Suit" and "Moby Dick" (1956); and "On the Beach" in 1959.
Peck continued to work steadily throughout the 1960s, starring in "The Guns of Navarone" (1961); "How the West Was Won" (1962); "Captain Newman, M.D." (1963); "Arabesque" (1966); "Mackenna's Gold" (1968); and "Marooned" (1969).
In 1977 he was nominated for a Golden Globe for Best Actor in a drama for his portrayal of U.S. military hero Douglas MacArthur in "MacArthur."