Olivia Newton-John, Pop Singer and ‘Grease’ Star, Dies at 73

Olivia Newton-John, who sang some of the biggest hits of the 1970s and ’80s while recasting her image as the virginal girl next door into a spandex-clad vixen — a transformation reflected in miniature by her starring role in “Grease,” one of the most popular movie musicals of its era — died on Monday at her ranch in Southern California. She was 73.

The death was announced by her husband, John Easterling. She had lived with a breast cancer diagnosis since 1992 and in 2017 announced that the cancer had returned and spread. For years she was a prominent advocate for cancer research, starting a foundation in her name to support it and opening a research and wellness center in metropolitan Melbourne, Australia. English-born, she grew up in Australia.

Ms. Newton-John amassed No. 1 hits, chart-topping albums and four records that sold more than two million copies each. More than anything else, she was likable, even beloved.

In the earlier phase of her career, Ms. Newton-John beguiled listeners with a high, supple, vibrato-warmed voice that paired amiably with the kind of swooning middle-of-the-road pop that, in the mid-1970s, often passed for country music.

Her performance on the charts made that blurring clear. She scored seven Top 10 hits on Billboard’s Country chart, two of which became back-to-back overall No. 1 hits in 1974 and ’75. First came “I Honestly Love You,” an earnest declaration co-written by Peter Allen and Jeff Barry, followed by “Have You Never Been Mellow,” a feather of a song written by the producer of many of her biggest albums, John Farrar.

“I Honestly Love You” also won two of the singer’s four Grammys, for record of the year and best female pop vocal performance.

The combination of Ms. Newton-John’s consistently benign music — she was never a favorite of critics — and comely but squeaky-clean image caused many writers to compare her to earlier blond ingénues like Doris Day and Sandra Dee. “Innocent, I’m not,” Ms. Newton-John told Rolling Stone in 1978. “People still seem to see me as the girl next door. Doris Day had four husbands,” she said, yet she was still viewed as “the virgin.”

An entry into movies in 1978 aimed to put the singer’s chaste image behind her, starting with “Grease.” Her character, Sandy, transformed from a pigtailed square smitten with John Travolta’s bad-boy Danny to a gum-smacking bad girl. “Grease” became one of the highest grossing movie musicals ever, besting even “The Sound of Music.” Its soundtrack was the second best-selling album of the year, beaten only by the soundtrack for “Saturday Night Fever,” which also starred Mr. Travolta.

The “Grease” soundtrack spawned two No. 1 hits, both sung by the co-stars, including the manically lusty “You’re the One That I Want” and the doo-wop romp “Summer Nights.” A ballad Ms. Newton-John sang alone, “Hopelessly Devoted to You,” earned the film’s lone Oscar nomination, for best song.

Applying the evolution of her “Grease” character to her singing career, Ms. Newton-John titled her next album “Totally Hot,” and presented herself on the cover in shoulder-to-toe leather. The album, released at the end of 1978, went platinum, yielding the rock-oriented “A Little More Love” with the line, “Where did my innocence go?”

The album featured Ms. Newton-John singing in a somewhat more forceful voice. Though her sales dipped as the 1970s turned into the ’80s, by early in the decade she began the most commercially potent period in her career, peaking with the single “Physical,” which spent 10 weeks on Billboard’s top perch. Later, the magazine declared it to be the biggest song of the 1980s.

Olivia Newton-John was born on Sept. 26, 1948, in Cambridge, England, the youngest of three children of Brinley and Irene (Born) Newton-John. Her mother was the daughter of the Nobel Prize-winning physicist Max Born. Her Welsh-born father had been an MI5 intelligence officer during World War II and afterward served as headmaster at Cambridgeshire High School for Boys.

When Ms. Newton-John was 6, her family immigrated to Melbourne, Australia, where her father worked as a college professor and administrator. At 14, she formed her first group, Sol Four, with three girls from school. Her beauty and confidence soon earned her solo performances on local radio and TV shows under the name “Lovely Livvy.” On “The Go!! Show” she met the singer Pat Carroll, with whom she would form a duet, as well as her eventual producer, Mr. Farrar, who later married Ms. Carroll.

Ms. Newton-John won a local TV talent contest whose prize was a trip to Britain. While tarrying there, she recorded her first single, “’Til You Say You’ll Be Mine,” which Decca Records released in 1966.

After Ms. Carroll moved to London, she and Ms. Newton-John formed the duet Pat and Olivia, which toured Europe. When Ms. Carroll’s visa expired, forcing her to go back to Australia, Ms. Newton-John stayed in London to work solo.

In 1970, she was asked to join a crudely manufactured group named Toomorrow, formed by the American producer Don Kirshner in an attempt to repeat his earlier success with the Monkees. Following his grand design, the group starred in a science-fiction film written for them and recorded its soundtrack. Both projects tanked.

“It was terrible, and I was terrible in it,” she later told The New York Times.

Her debut solo album, “If Not for You,” was released in 1971, its title track a cover of a Bob Dylan song.

After some duds in the United States, Ms. Newton-John released the album “Let Me Be There” (1973), which led to a Grammy win for best female country vocal performance.

Two key changes in pop music boosted her career that decade: the rise of “soft rock” in reaction to the harder genres of the late 1960s, and the mainstreaming — some would say the neutering — of country music, also epitomized by stars like John Denver and Anne Murray.

The latter trend became an issue in 1974, after Ms. Newton-John was chosen female vocalist of the year by the Country Music Association over more traditional stars like Loretta Lynn and Dolly Parton. Protests led to the formation of the fleeting Association of Country Entertainers. Yet, after Ms. Newton-John recorded her “Don’t Stop Believin’,” album in Nashville in 1976, the friction eased.

The second phase of her career, which began with “Grease,” found further success through a duet with Andy Gibb, “I Can’t Help It,” followed by an attempt to expand her acting career with the 1980 musical film “Xanadu,” with Gene Kelly. While the movie floundered, its soundtrack went double-platinum, boasting hits like “Magic” (which commanded Billboard’s No. 1 spot for four weeks) and the title song, recorded with the Electric Light Orchestra.

A campy Broadway show based on the film opened in 2007 to some success.

Ms. Newton-John’s smash “Physical” also yielded the first video album to hit the market, with clips for all the album’s tracks. “Olivia Physical” won the Grammy in 1982 for video of the year.

She was paired again with Mr. Travolta in the 1983 movie “Two of a Kind,” an attempt to repeat the success of “Grease.” But the film disappointed even as its soundtrack proved popular, especially the song “Twist of Fate.”

Ms. Newton-John was named an officer of the Order of the British Empire in 1979.

By the mid-’80s, her career had cooled. For several years she cut back on work to care for her daughter, Chloe Rose, whom she had with her husband at the time, the actor Matt Lattanzi. They had met on the set of “Xanadu” and married in 1984; they divorced in 1995.

That same year, she met Patrick McDermott, a cameraman whom she dated, on and off, for the next nine years. In 2005, Mr. McDermott disappeared while fishing off the California coast. Ms. Newton-John was never a suspect in his disappearance. Three years later, a U.S. Coast Guard investigation said that the evidence suggested that Mr. McDermott had been lost at sea.

In 2008, Ms. Newton-John married Mr. Easterling, the founder of the Amazon Herb Company.

In addition to her husband, she is survived by her daughter, Chloe Rose Lattanzi; her sister, Sarah Newton-John; and her brother, Toby.

After learning she had breast cancer in 1992, Ms. Newton-John became an ardent advocate for research into the disease. Her Olivia Newton-John Foundation Fund is dedicated to researching plant-based treatments for cancer, and she opened a cancer research and wellness facility under her name at Austin Hospital, outside Melbourne.

Despite her own treatments, she continued to release albums and tour but failed to make headway on the charts. And she continued to act in movies and on television.

In May 2017, she disclosed that her cancer had returned and that it had metastasized to her lower back. She published a memoir, “Don’t Stop Believin,’” in 2018.

To the end Ms. Newton-John firmly believed in her audience-friendly approach to music. “It annoys me when people think because it’s commercial, it’s bad,” she told Rolling Stone. “It’s completely opposite. If people like it, that’s what it’s supposed to be.”