Sinead O’Connor, the outspoken Irish singer-songwriter best known for her powerful, evocative voice, as showcased on her biggest hit, a breathtaking rendition of Prince’s “Nothing Compares 2 U,” and for her political provocations onstage and off, has died. She was 56.

Her family announced the death in a statement, according to the BBC and the Irish public broadcaster RTE. “It is with great sadness that we announce the passing of our beloved Sinead,” the statement said. “Her family and friends are devastated and have requested privacy at this very difficult time.” No other details were provided.

Recognizable by her shaved head and by wide eyes that could appear pained or full of rage, Ms. O’Connor released 10 studio albums, beginning with the alternative hit “The Lion and the Cobra” in 1987. She went on to sell millions of albums worldwide, breaking out with “I Do Not Want What I Haven’t Got” in 1990.

That album, featuring “Nothing Compares 2 U,” a No. 1 hit and MTV staple, won a Grammy Award in 1991 for best alternative music performance — although Ms. O’Connor boycotted the ceremony over what she called the show’s excessive commercialism.

Ms. O’Connor rarely shrank from controversy, though it often came with consequences for her career.

In 1990, she threatened to cancel a performance in New Jersey if “The Star-Spangled Banner” was played at the concert hall ahead of her appearance, drawing the ire of no less than Frank Sinatra. That same year, she backed out of an appearance on “Saturday Night Live” in protest of the misogyny she perceived in the comedy of Andrew Dice Clay, who was scheduled to host.

But all of that paled in comparison to the uproar caused when Ms. O’Connor, appearing on “S.N.L.” in 1992 — shortly after the release of her album “Am I Not Your Girl?” — ended an a cappella performance of Bob Marley’s “War” by ripping a photo of Pope John Paul II into pieces as a stance against sexual abuse in the Roman Catholic Church. “Fight the real enemy,” she said.

That incident immediately made her a target of criticism and scorn, from social conservatives and beyond. Two weeks after her “S.N.L.” appearance, she was loudly booed at a Bob Dylan tribute concert at Madison Square Garden.

For a time, the pileup of vitriol directed at Ms. O’Connor was so pervasive that it became a kind of pop-culture meme in itself. On “S.N.L.,” Madonna mocked the incident by tearing up a picture of Joey Buttafuoco, the Long Island auto mechanic who was a tabloid fixture at the time because of his affair with a 17-year-old girl.

Once a rising star, Ms. O’Connor stumbled in the wake of the incident. “Am I Not Your Girl?,” an album of jazz songs and standards like “Why Don’t You Do Right?” and “Bewitched, Bothered and Bewildered,” was stalled on the charts at No. 27. Her next album, “Universal Mother” (1994), went no higher than No. 36.

Ms. O’Connor never had another major hit in the United States after “The Emperor’s New Clothes,” from “I Do Not Want What I Haven’t Got,” although for a time she remained a staple on the British charts.

But in her 2021 memoir, “Rememberings,” Ms. O’Connor portrayed her act of ripping up the photo of the pope as a righteous act of protest — and thus a success.

“I feel that having a No. 1 record derailed my career,” she wrote, “and my tearing the photo put me back on the right track.”

She elaborated in an interview with The New York Times that same year, calling the incident an act of defiance against the constraints of pop stardom.

“I’m not sorry I did it. It was brilliant,” Ms. O’Connor said. “But it was very traumatizing,” she added. “It was open season on treating me like a crazy bitch.”

Ms. O’Connor was born in Dublin on Dec. 8, 1966. Her father, John, was an engineer, and her mother, Johanna, was a dressmaker.

In interviews, and in her memoir, Ms. O’Connor spoke openly of a traumatic childhood. She said that her mother physically abused her and that she was deeply affected by her parents’ separation, when she was 8. She was arrested for shoplifting and sent to reform schools.

At 15, at a wedding, she sang “Evergreen” — the love theme from “A Star Is Born,” made famous by Barbra Streisand — and was discovered by Paul Byrne, a drummer who had an affiliation with the superstar Irish band U2. She left boarding school at 16 and began her career, supporting herself by waitressing and performing “kiss-o-grams” in a kinky French maid costume.

“The Lion and the Cobra” — the title is an allusion to Psalm 91 — marked her as a rising talent with a spiritual heart, an ear for offbeat melody and a fierce and combative style.

She drew headlines for defending the Irish Republican Army, fired her manager and publicly mocked U2 as “bombastic.” She also said she had rejected attempts by her record company, Ensign, to adopt a more conventional image.

The leaders of Ensign “wanted me to wear high-heel boots and tight jeans and grow my hair,” Ms. O’Connor told Rolling Stone in 1991. “And I decided that they were so pathetic that I shaved my head so there couldn’t be any further discussion.”

“Nothing Compares 2 U” — originally released by the Family, a Prince side project, in 1985 — became a phenomenon when Ms. O’Connor released it five years later. The video for the song, trained closely on her emotive face, was hypnotic, and Ms. O’Connor’s voice, as it raised from delicate, breathy notes to powerful cries, stopped listeners in their tracks.

Not long after the song became a hit, Ms. O’Connor accused Prince of physically threatening her. She elaborated on the story in her memoir, saying that Prince, at his Hollywood mansion, chastised her for swearing in interviews and suggested a pillow fight, only to hit her with something hard that was in his pillowcase. She escaped on foot in the middle of the night, she said, but Prince chased her around the highway.

As her music career slowed, Ms. O’Connor, who had been open in the past about her mental health struggles, became an increasingly erratic public figure, often sharing unfiltered opinions and personal details on social media.

In 2007, she revealed on Oprah Winfrey’s television show that she had been diagnosed with bipolar disorder and that she had tried to kill herself on her 33rd birthday. Her son Shane died by suicide in 2022, at 17.

Ms. O’Connor said in 2012 that she had been misdiagnosed and that she was suffering from post-traumatic stress disorder stemming from a history of child abuse. “Recovery from child abuse is a life’s work,” she told People magazine.

Several years ago she converted to Islam and started using the name Shuhada Sadaqat, though she continued to answer to O’Connor as well.

Information on survivors was not immediately available.

In discussing her memoir with The Times in 2021, Ms. O’Connor focused on her decision to tear up the photo of John Paul II as a signal moment in a life of protest and defiance.

“The media was making me out to be crazy because I wasn’t acting like a pop star was supposed to act,” Ms. O’Connor said. “It seems to me that being a pop star is almost like being in a type of prison. You have to be a good girl.”