Christine McVie, the British-born Fleetwood Mac vocalist, songwriter, and keyboardist whose cool, soulful contralto helped define hits like “You Make Loving Fun,” “Everywhere,” and “Don’t Stop,” died on Wednesday at the age of 79.

Her passing was announced on the band’s social media pages. There was no immediate word on the cause of death or other details, but a family statement said she “passed away peacefully at the hospital this morning” with family by her side after a “short illness.”

“I was told a few hours ago that my best friend in the entire world since the first day of 1975 had passed away,” bandmate Stevie Nicks said in a handwritten note on Instagram.

She went on to say that one song has been “swirling around” in her head since learning of McVie’s illness, quoting the lyrics to HAIM’s “Hallelujah”: “I had a best friend/But she has passed.”

McVie was a consistent presence and personality in a band known for frequent lineup changes and volatile personalities, most notably fellow singer-songwriters Nicks and Lindsey Buckingham.

Christine’s death is the first among Fleetwood Mac’s most famous incarnations of McVie, Nicks, Buckingham, drummer Mick Fleetwood, and ex-husband, bassist John McVie. The band has toured without Buckingham in recent years after he was fired in 2018 and replaced on stage by Mike Campbell and Neil Finn.

Fleetwood Mac began in the 1960s as a London blues band and evolved into one of the defining makers of 1970s California pop-rock, with McVie, Nicks, and Buckingham anchoring the rhythm section of Fleetwood and John McVie.

From 1975 to 1980, the band sold millions of records and captivated fans by transforming personal battles into melodic, compelling songs. The McVies’ breakup and Nicks and Buckingham’s were famously documented on the 1977 album “Rumours,” which became one of the best-selling albums of all time.

Fleetwood and John McVie formed a deep and bluesy groove, Buckingham was the resident mad genius and perfectionist, Nicks was the charismatic dramatist and idol to countless young women, and Christine McVie was the grounded counterpoint, her economy as a singer and player well suited to her birth surname: Perfect.

“I was supposedly like Mother Teresa, hanging out with everyone or just trying to (keep) everything nice and cool and relaxed,” she told Rolling Stone earlier this year. “But they were wonderful people and wonderful friends.”

When Fleetwood Mac was inducted into the Rock and Roll Hall of Fame in 1998, they performed McVie’s “Say You Love Me.” Other hit singles by the group included Nicks’ “Dreams,” Buckingham’s “Go Your Way,” and McVie’s “Little Lies.” The thoughtful ballad “Songbird,” one of McVie’s most beloved works, was a showcase for her in concert and was covered by Willie Nelson, among others.

The midtempo rocker “Don’t Stop,” inspired by her divorce, would gain unexpected political relevance when Bill Clinton adopted the song — and its refrain “Don’t stop thinking about tomorrow” — as a theme for his 1992 presidential campaign. The band, which had essentially stopped making albums then, reformed for his inauguration gala performance.

McVie’s two marriages, to John McVie and Eduardo Quintela, were both annulled. Dennis Wilson of the Beach Boys was one of her boyfriends, and she wrote “Only Over You” about him.

Christine Anne Perfect McVie was born in Bouth, Lancashire, into a musical family. Her father was a violinist and music teacher, and her grandfather was a Westminster Abbey organist. She had been studying the piano since childhood, but she abandoned her classical studies after hearing early rock records by Fats Domino and others.

She befriended various members of Britain’s emerging blues scene while studying at the Moseley School of Art, and in her twenties, she joined the band Chicken Shack as a singer and pianist. Among the rival bands she admired was Fleetwood Mac, which featured blues guitarist Peter Green and the rhythm section of Fleetwood and John McVie at the time. She had joined the group and married John McVie by 1970.

Against all odds, few bands have done as well as Fleetwood Mac, which has sold over 100 million records. Green was one of many performers who left the band, and Fleetwood Mac appeared to be on the verge of disbanding or fading away at various points. It was saved by unexpected returns, interventions, and one of rock’s most fortunate and profitable hunches.

Fleetwood Mac was reduced to three members in the mid-1970s: Fleetwood and the two McVies. While in Los Angeles, Fleetwood became aware of a young California duo, Buckingham and Nicks, who had recorded the little-known album “Buckingham Nicks.” Impressed by their sound, he planned to invite only Buckingham, but the guitarist insisted on including Nicks, his girlfriend.

The new lineup was almost immediately magical. Nicks and Christine McVie formed a lifelong friendship, agreeing that as two of rock’s few female rock stars, they would always be there for each other. And the harmonies and music of Nicks, Buckingham, and Christine McVie ensured that albums like “Fleetwood Mac,” “Rumours,” and “Mirage” had an enviable level of quality and variety of songwriting and vocal styles.

However, the group’s overwhelming success inevitably resulted in conflicts and a desire for solo work. Nicks rose to prominence in the decades that followed. McVie released solo albums such as “Christine McVie” and “Christine Perfect,” as well as “Lindsey Buckingham/Christine McVie,” a 2017 collaboration with Buckingham.