As a suave and dignified star, Mr. Poitier challenged audiences to accept Black performers in leading roles in movies and on television. He upended a demeaning Hollywood tradition of casting Black performers in vulgar caricature or limiting them to singing and dancing roles that could be segregated from the rest of the film and cut out when the movies ran in the South.

Mr. Poitier’s Oscar was for “Lilies of the Field,” a film released in 1963 — the same year as the March on Washington for civil rights. By contrast, the film, about a drifter handyman who helps nuns from Central Europe build a chapel in Arizona, made almost no mention of race, which Mr. Poitier, who championed colorblind casting, deemed as much a triumph as his Oscar.

Perhaps his most enduring and defining part was Virgil Tibbs, an experienced Philadelphia homicide detective who helps a bigoted White Mississippi police chief in a murder investigation in “In the Heat of the Night” (1967). The film marked the first appearance of a Black law enforcement hero in a mainstream Hollywood movie.

“In the original script, I looked at him with great disdain and, wrapped in my strong ideals, walked out,” he wrote. “That could have happened with another actor playing the part, but it couldn’t happen with me.” He insisted on a change to the script because of a searing experience as a teenager in Florida, when police stopped him for walking in a White neighborhood. “They really had their fun with me,” he recalled in the book. “They put a pistol right to my forehead. . . . And for 10 minutes, they just joked about whether to shoot me in the right eye or left eye.”

Mr. Poitier’s place in the 1960s Hollywood hierarchy — a major star with critical and popular appeal — was exceptional in the ranks of Black actors. Harry Belafonte, a popular singer of calypso and other folk songs, exuded more sexual charisma than Mr. Poitier but lacked his range. Belafonte tried to make it as a leading man in the 1950s before returning to a career in music and civil rights.

After his Academy Award win, Mr. Poitier said he doubted that the honor would be a “magic wand that will wipe away the restrictions on job opportunities for Negro actors.” Even at his career’s peak, in the 1960s, he said his creative control was often limited to rejecting roles that he felt were unworthy.

But the thoughtful, unthreatening image he projected — playing a doctor engaged to a White woman in “Guess Who’s Coming to Dinner” and a London teacher who tames rowdy students in “To Sir, With Love” (both 1967) — was out of step with increasingly assertive Black activism. In some quarters, Mr. Poitier came under withering attack.

Writer Larry Neal was among the Black activists and artists to scold Mr. Poitier, calling him in 1971 “a million-dollar shoeshine boy.” Melvin Van Peebles, who made the politically radical film “Sweet Sweetback’s Baadasssss Song” (1971), wrote decades later in Ebony magazine, “Sidney was a wonderful actor, and we were proud, but nobody could really relate because the characters he was given to play were surreal, more from heaven than the ’hood.”

Film critic and scholar Richard Schickel said many in the Black community, as well as some White movie critics, wanted Mr. Poitier “to lead the revolution in the movies. But in truth, the movies were somewhat behind the ‘revolutionary curve.’ So what was on offer for Mr. Poitier was being a middle-class guy who, to a degree, challenged White smugness.”

After being off the movie big screen for 10 years, Mr. Poitier returned in a pair of action thrillers in 1988, playing FBI agents in “Shoot to Kill” and “Little Nikita.” Four years later, Mr. Poitier was lured back to portray a cashiered CIA agent in “Sneakers” (1992), with Robert Redford and Dan Aykroyd, because “it was a wonderful, breezy opportunity to play nothing heavy. It was simple, and I didn’t have to carry the weight. I haven’t done that in a while, and it was refreshing.”

He became a physiotherapist at an Army psychiatric institution on Long Island, but his anger at what he called the “abusive” attitude toward the patients and the racism he encountered at a local roadhouse antagonized him. Through the intervention of a sympathetic doctor, he received an honorable discharge.

At his audition, Mr. Poitier’s unintelligible, singsong island accent dismayed theater founder Frederick O’Neal. But O’Neal was in such dire need of male actors that Mr. Poitier was hired with the understanding that he would also moonlight as the theater’s janitor. (To polish his speaking, he bought a radio and studied the diction and intonation of the announcers.)

During his first Broadway appearance, a small part in a 1946 production of Aristophanes’ ancient Greek comedy “Lysistrata,” Mr. Poitier suffered stage fright and began delivering lines out of order. But citing his “terrible fierce pride,” he later said he was determined to refine his skills. Over the next several years, his good looks and sensitivity as a performer brought him to the attention of Hollywood, and he made a strong impact in “No Way Out,” his film debut.

In his second feature film, Mr. Poitier was cast as a young clergyman in “Cry, the Beloved Country” (1951), based on Alan Paton’s novel about apartheid. Working on location in South Africa, Mr. Poitier was forced to live far from the studio, and he had to deal with other restrictions and insults. Officially, he was an “indentured laborer” of director Zoltan Korda. Mr. Poitier later called South Africa “on a racial, political and social level, the worst place I have ever been.”

After that brush with glory, Mr. Poitier said he felt forced to take a leap backward in the 1959 film version of the George and Ira Gershwin-DuBose Heyward folk operetta “Porgy and Bess.” Porgy, he said, was an embarrassingly “outdated” part. But Samuel Goldwyn insisted on having him, and Mr. Poitier said it would have been a career-ending move to refuse such a powerful producer. (Mr. Poitier’s songs were dubbed by opera singer Robert McFerrin, the father of singer Bobby McFerrin.)

Not long after, he read the script for “Lilies of the Field,” and he knew immediately that it was the type of part that most intrigued him: a showcase for his magnetism that did not have to make overt statements about skin color. It also seemed a decidedly uncommercial undertaking, utterly lacking in romance or action.

Mr. Poitier became the third Black recipient of an Oscar in an acting category. Previous winners were Hattie McDaniel, for her supporting role as the enslaved Mammy in “Gone With the Wind” (1939), and James Baskett, who received a special award for playing Uncle Remus in Walt Disney’s “Song of the South” (1946).

The last — about an interracial couple whose nuptials are opposed by the parents on both sides — had the distinction of not ending tragically. But at one point, Mr. Poitier tells his screen father, “You think of yourself as a colored man. I think of myself as a man,” a line that typified what Mr. Poitier’s more militant critics found troubling about his roles.

In 2002, Mr. Poitier received a lifetime achievement Oscar for “his extraordinary performances and unique presence on the screen and for representing the industry with dignity, style and intelligence.” That year, Denzel Washington became the second Black man to win the best-actor Oscar, for his role in the police drama “Training Day.”

“I was part of an influence that could be called paving the way,” he told the Times of London in 1992. “But I was only a part of it. I was selected almost by history itself. Most of my career unfolded in the 1960s, which was one of the periods in American history with certain attitudes toward minorities that stayed in vogue.”