She was by far best known for “Laverne & Shirley,” the “Happy Days” spinoff that ran on ABC from 1976 to 1983 that in its prime was among the most popular shows on TV.
Ms. Williams played the strait-laced Shirley Feeney to Marshall’s more libertine Laverne DeFazio on the show about a pair of blue-collar roommates who toiled on the assembly line of a Milwaukee brewery in the 1950s and ’60s.
DeFazio was quick-tempered and defensive; Feeney was naive and trusting. The actors drew upon their own lives for plot inspiration.
“We’d make up a list at the start of each season of what talents we had,” Marshall told the Associated Press in 2002. “Cindy could touch her tongue to her nose, and we used it in the show. I did tap dance.”
The series was the rare network hit about working-class characters, with its self-empowering opening song: “Give us any chance, we’ll take it, read us any rule, we’ll break it.”
That opening would become as popular as the show itself. Ms. Williams’ and Marshall’s chant of “schlemiel, schlimazel” as they skipped together became a cultural phenomenon and oft-invoked piece of nostalgia.
Marshall, whose brother, Garry Marshall, co-created the series, died in 2018.
The show also starred Michael McKean and David Lander as Laverne and Shirley’s oddball hangers-on Lenny and Squiggy. Lander died in 2020.
As ratings dropped in the sixth season, the characters moved from Milwaukee to Burbank, Calif., trading their brewery jobs for work at a department store.
In 1982, Ms. Williams became pregnant and wanted her working hours curtailed. When her demands weren’t met, she walked off the set and filed suit against its production company. She appeared infrequently during the final season.
Cynthia Williams was born one of two sisters in the Van Nuys area of Los Angeles on Aug. 22, 1947. Her mother was a waitress, and her father was an electronics technician who uprooted the family to Texas for several years to try farming before returning to Southern California.
She was drawn to acting as an escape from an unhappy and violent childhood and into a world of happy suburban sitcom families.
“I was a kid with an alcoholic father whose parents would get in violent fights,” she told the Waterloo Region Record. “And I’d be watching ‘My Little Margie’ or ‘Your Show of Shows,’ and they would take me away. It was ‘forget your troubles — come on, get happy.’”
Ms. Williams majored in theater arts at Los Angeles City College and began winning TV roles in the late 1960s. Producer Ross Hunter became one of her key early supporters, saying she had an understated quality that made audiences identify with her.
She appeared in the film “Travels With My Aunt” (1972), directed by George Cukor. But her part in “American Graffiti,” a cinematic forerunner to a nostalgia boom for the 1950s and early 1960s that would follow, would help lead to her defining TV role.
“Happy Days,” starring her “American Graffiti” co-star Ron Howard, would premiere the following year. The characters of Laverne and Shirley made their first TV appearance as dates of Henry Winkler’s Fonzie before they got their own show.
In the past three decades, Ms. Williams made guest appearances on dozens of TV series including “7th Heaven,” “8 Simple Rules” and “Law and Order: Special Victims Unit.” In 2013, she and Marshall appeared in a “Laverne & Shirley” tribute episode of the Nickelodeon series “Sam and Cat.”
Last year, Ms. Williams appeared in a one-woman stage show full of stories from her career, “Me, Myself and Shirley,” at a theater in Palm Springs, Calif., near her home in Desert Hot Springs.
Her marriage to singer Bill Hudson of musical group the Hudson Brothers ended in divorce. He was previously married to Goldie Hawn and is also the father of actor Kate Hudson. Ms. Williams had two children, but a complete list of survivors was not immediately available.