Budd Schulberg, a screenwriter, novelist and journalist who was a longtime Vineyard summer resident, died on August 5 at his home in Westhampton Beach, N.Y., of natural causes. He was 95.

Best known for writing the screenplay of On the Waterfront, for which he won an Academy Award, Mr. Schulberg was a prolific writer of novels, including the best-selling What Makes Sammy Run?, screenplays, nonfiction books, articles on boxing, a Broadway musical and a Broadway play. The New York Times in its obituary called him legendary. In both his creative and nonfiction work he argued for social and political justice, and in his private life he worked to foster the same goals, starting the Watts Writers’ Workshop in the wake of the Watts riots to recognize and train artistic voices from the Los Angeles ghetto, and cofounding the Frederick Douglass Creative Arts Center in New York, which he continued to work for until his death.

Mr. Schulberg had strong Vineyard connections through both his sister, Sonya, who with her husband Ben O’Sullivan started spending summers here in 1949, and through his wife, Betsy Anne Langman Schulberg. Mr. Schulberg himself first came to the Vineyard, renting a cottage in Menemsha, in 1950 with his second wife, Victoria, their sons Steven and David, and his daughter from his first marriage, Victoria. He was married to the actress Geraldine Brooks from 1964 until her death in 1977. After his marriage in 1978 to Betsy, whose family has long owned a house in Menemsha, Salt Meadows, he returned regularly with her and their children, Benn and Jessica.

He is survived by Betsy and all his children except David, a Viet Nam veteran who died in 2007; by his sister of West Tisbury and Mamaroneck, NY; by his daughter Victoria’s two children and two grandchildren; by Sonya’s two children, John and Chris O’Sullivan, and two grandchildren; by Sandra, K.C., Peter, and Jonathan Schulberg, the children of his younger brother and collaborator, Stuart, who died in 1979, and their five children; and by Betsy’s siblings Tom Langman, Lynn Lilienthal, and Debby Lesser, and their nine children.

Budd Schulberg was born in New York city but raised in Hollywood, where his father, B.P. Schulberg, was one of the founders of the modern movie industry, rising to become head of production at Paramount Studios during the era of silent movies and early talkies. The movie industry did very well during the Depression, and both the stark contrasts of rich and poor that he saw, as well as the overnight rise — and fall — of people’s careers in the movie business left strong marks on Mr. Schulberg, as did his exposure to prizefighting through his father, who often took him to boxing matches. One of those who rose, then fell, was Mr. Schulberg’s father. After B.P. Schulberg lost his position at Paramount and his fortune, his ex-wife, Adeline Schulberg, became the first notable woman talent agent, with offices in Los Angeles and London. After World War II ruined her business, she became a New York literary agent representing, among others, her son.

Mr. Schulberg was a summa cum laude graduate of Dartmouth, where he was also the editor of the student newspaper. After college, he returned to Hollywood, working as a junior writer with Ring Lardner on A Star Is Born. He was then assigned to write a screenplay based on Dartmouth’s Winter Carnival. The producer didn’t like the initial script and hired F. Scott Fitzgerald to work with Schulberg. The two went to Hanover to get the flavor of the place, but Fitzgerald went on such a binge that they were fired before returning to California. That later served as the basis for Mr. Schulberg’s best-selling novel The Disenchanted, which was also made into a Broadway play for which Jason Robards won a Tony Award for playing the Fitzgerald character.

Mr. Schulberg’s first novel, published in 1941, was What Makes Sammy Run?, the story of a ruthless newspaper errand boy, Sammy Glick, who becomes a wealthy film producer. “Going through life with a conscience,” Sammy says, “is like driving your car with the hand brake on.” Mr. Schulberg’s father had warned him that publishing a scathing book on ethics in Hollywood could lead to his being ostracized, and in fact there was widespread anger about the book in the film community. In addition, Mr. Schulberg split with the Communist Party in part over the book, which the party tried to censor. The novel was a huge success, however, going through 10 printings in the first year.

Mr. Schulberg served in the Navy during World War II, and like many sons of Hollywood, worked both in film and in the OSS, the precursor to the CIA. He served under director John Ford, and was assigned, with his younger brother Stuart, to gather film to use as evidence at the Nuremberg war crimes trials. Initially, he gathered film from Allied sources, but was told by prosecutors that they would only use footage from German sources, since it would not be suspect as propaganda. As Mr. Schulberg related at a 2005 forum at the Holocaust Museum in Washington, that task became a race between his team and Nazis to see whether he could locate and seize film before those seeking to protect the defendants could find the film and burn it. In the process, he interrogated and arrested Nazi filmmaker Leni Riefenstahl. In the end, he and his team put together over four hours of incriminating Nazi film that was introduced at the first Nuremberg trial.

Upon his return from the war, Mr. Schulberg wrote another best-seller, The Harder They Fall, about a boxing writer who becomes a corrupt fight promoter. He coauthored the screenplay, and Humphrey Bogart played the promoter in his final film role.

In a highly controversial move, Mr. Schulberg testified before the House Un-American Activities Committee in 1951. He named other members of the Communist Party, though none that had not been previously identified, and said that he broke with the party over both Stalin’s pact with Hitler and the party’s attempt at censorship. In an interview with the Hollywood Reporter in 2000, he said, “My own feeling was that while I didn’t like the committee’s being so right-wing, I didn’t think it was healthy having a secret organization trying to control the Writers Guild. I felt it was wrong and undermining democracy.”

After writing The Disenchanted, Mr. Schulberg next wrote the original screenplay for On the Waterfront, the work for which he was best known. The 1954 Academy Award winner for Best Picture, the film was directed by Elia Kazan and starred a young Marlon Brando and Eva Marie Saint, all of whom won Oscars, as did Mr. Schulberg. The film was so influential that it was selected for preservation in the United States National Film Registry by the Library of Congress, and the line “I coulda been a contender” became a part of the national language.

The director and writer teamed up again for the 1957 film A Face in the Crowd, adapted from a Schulberg short story. The Washington Post called the movie “an underrated gem, a perceptive look at the future of television and politics.” The film featured Andy Griffith, in what many regard as his best role, as a country singer who becomes a power-hungry demagogue. The movie’s influence continues: Spike Lee dedicated Bamboozled, his 2000 film that satirized television, to Mr. Schulberg. They were also working together on a screenplay about Joe Louis.

Mr. Schulberg’s fame with On the Waterfront led then-Attorney General Robert F. Kennedy to ask him to write the screenplay of The Enemy Within, his book about exposing labor racketeers. That movie was never made, but it influenced Mr. Schulberg’s novel Everything That Moves” (1980), a veiled account of Kennedy’s hearings on Teamster leader Jimmy Hoffa. The two men remained close. Mr. Schulberg was a few steps behind Robert Kennedy in the kitchen of the Ambassador Hotel in Los Angeles in 1968 when he was shot, and he helped wrest the gun from Kennedy’s assassin, Sirhan Sirhan.

Throughout his life, Mr. Schulberg was also a popular boxing authority. He was the first boxing editor of Sports Illustrated magazine, and wrote for the first issue. (The title of his collection of short stories, Faces in the Crowd, was also borrowed by Sports Illustrated for its feature entitled Some Faces in the Crowd.) He was friends with numerous boxers, including heavyweight champion Floyd Patterson and light heavyweight champion Jose Torres, and helped Torres become a writer. He supported heavyweight champion Muhammad Ali’s right to defend his title after being stripped of it when Ali would not fight in the Viet Nam War. In 1972, he wrote a well-received biography of Ali, Loser and Still Champion. He is the only non-boxer the World Boxing Association has named as a living legend of boxing.

He remained an active and prolific writer until his death. He covered boxing matches and worked on and attended adaptations of his work, as recently as two months ago in London and the week before his death in Hoboken. He was writing a second volume of his autobiography, having written about growing up in Hollywood in Moving Pictures, published in 1981, and was involved in several other projects as well.

There was a small ceremony for family and friends at the family house in Westhampton Beach on August 9. A larger memorial is planned for New York city in mid-September. In lieu of flowers, the family has asked that donations be made to the Frederick Douglass Creative Arts Center, 270 W. 96th street, New York, NY 10024.