Bobby Keys, a Texas-born saxophonist who spent decades performing as a sideman with the Rolling Stones, supplying high-energy solos to “Brown Sugar” and other hits, but whose undisciplined behavior became too outrageous even for the fast-living rockers, died Dec. 2 at his home in Franklin, Tenn. He was 70.

The Rolling Stones confirmed his death in a statement. The cause was cirrhosis of the liver, according to the Nashville Scene newspaper.

A self-taught musician who never learned to read music, Mr. Keys brought a full-bodied, open-throttle sound to everything he played. He first worked with the Stones in 1969, during the recording of the “Let It Bleed” album, and was immediately drawn to the raw spirit of the band’s music. He became a frequent musical partner in the Stones’ recordings and concerts for more than 40 years.

His powerful tenor-sax solo on the 1971 hit “Brown Sugar,” which Mr. Keys recorded in a single take, became an indelible part of the Stones’ musical legacy. He made major contributions to dozens of other tunes, including “Honky Tonk Women” and “Can’t You Hear Me Knocking,” and appeared on many of the band’s most celebrated albums, such as “Sticky Fingers” (1971), “Exile on Main Street” (1972) and “Some Girls” (1978).

Mr. Keys had the same birthday as Keith Richards, the Stones’ guitarist and founding member, and the two shared an interest in other activities besides music. In his 2010 autobiography, “Life,” Richards called Mr. Keys “my closest pal. A soul of rock ’n’ roll, a solid man, also a depraved maniac.”

Bobby Keys at a recording session in the 1970s. (Photo by Estate Of Keith Morris/Redferns/Getty Images)

Besides his hard-hitting saxophone performances, Mr. Keys became known for his unabashed indulgence in the rock-and-roll life. In 2010, he recalled to the Observer newspaper in Britain the scene in France while the Stones were making “Exile on Main Street.”

“Hell, yeah, there was some pot around,” he said, “there was some whiskey bottles around, there was scantily clad women. Hell, it was rock-and-roll!”

Mr. Keys and Richards were infamously captured on film in 1972 when they threw a television out of a hotel window. But Mr. Keys’s heavy drinking and addiction to heroin made him undependable on stage, and he missed rehearsals and other engagements. The final straw reputedly came when Richards found him lounging with a woman in a bathtub filled with champagne when he should have been ready to play. He was dismissed from the Rolling Stones in 1973.

He made occasional appearances with the band, but it wasn’t until the 1980s, when Richards sneaked Mr. Keys into a rehearsal, that the reunion was complete. While the band ran through “Brown Sugar,” an unseen Mr. Keys wailed his barn-burning solo. According to Richards, Mick Jagger’s jaw dropped as he turned and said, “What the . . . ?”

From that point on, Mr. Keys was back with the Stones.

Robert Henry Keys was born in Slaton, Tex., on Dec. 18, 1943 — the same day and year as Richards. He was raised largely by his grandparents.

He often visited an aunt who lived in Lubbock, Tex., near the home of the rock guitarist and singer Buddy Holly. Mr. Keys recalled hearing Holly and his band, the Crickets, playing for the opening of a gas station.

“That did it for me,” he told Texas Monthly in 2012. “Rock and roll was calling, and I said, ‘Here I am.’ ”

Inspired by King Curtis, the saxophonist on the Coasters’s hit “Yakety Yak,” Mr. Keys taught himself to play the saxophone and was working professionally by age 15.

“ ’Cause I can’t read music,” Mr. Keys told Rolling Stone, “I have no idea what’s gonna come out of that horn half the time. . . . I come strictly from feeling, and that feeling comes from rock-and-roll.”

In the early 1960s, Mr. Keys toured with singer Bobby Vee. Over the years, he recorded with B.B. King, Joe Cocker, Barbra Streisand, Carly Simon, Lynyrd Skynyrd, The Who, Eric Clapton and all four members of the Beatles after their breakup.

Mr. Keys reportedly was married at least five times and had two children. A complete list of survivors could not be confirmed.

After serving as the music director in the late 1980s at a nightclub in Miami Beach, Fla., owned by Rolling Stones guitarist Ron Wood, Mr. Keys settled outside Nashville. He published a memoir, “Every Night’s a Saturday Night,” in 2012 and continued to perform with the Stones and other groups until this year.

Mr. Keys admitted that he was “a devout pothead” who had been smoking marijuana since his teens.

“I never let a day go by,” he once told Rolling Stone magazine, “unless I’m in jail.”

An earlier version of this story incorrectly identified saxophonist King Curtis as King Pleasure. It also stated that Mr. Keys played the saxophone solo on the Rolling Stones song “Miss You.” Mel Collins played the saxophone solo on the original 1978 recording of the song; Mr. Keys played it in later concerts with the band.