Paul Smith, a jazz pianist who accompanied many top singers and who provided the sensitive touch and rhythmic spark behind many of Ella Fitzgerald’s most acclaimed performances, died June 29 at a hospital in Torrance, Calif. He was 91.

He had cancer and died of heart ailments, his publicist, Alan Eichler, said.

Mr. Smith, whose career lasted more than 70 years, worked with two of the biggest musical acts of the 1940s, the Andrews Sisters and the Tommy Dorsey Orchestra, before settling in Hollywood, where he performed on the soundtracks of hundreds of films and television shows.

He stood an imposing 6-foot-5 and could span 12 notes on the piano with each hand. Despite his physique, Mr. Smith was known for a delicate touch at the keyboard that few could match. He made more than 50 recordings as a leader of his own groups, but he spent much of his career working in the shadow of such top-flight singers as Sarah Vaughan, Nat “King” Cole, Doris Day, Bing Crosby, Jo Stafford, Rosemary Clooney, Anita O’Day and Sammy Davis Jr.

Mr. Smith’s most significant association was with Fitzgerald, the jazz singer he accompanied on and off from 1956 to 1990. Fitzgerald’s biographer, Stuart Nicholson, called Mr. Smith “a massively accomplished pianist who at the time was perhaps the studio musician most in demand on the West Coast.”

Pianist Paul Smith is shown with his wife, singer-pianist Annette Warren. She did the singing part for Ava Gardner in the 1951 movie “Show Boat.” (Courtesy of Paul Smith and Annette Warren) (Courtesy of Paul Smith and Annette Warren)

He was the pianist on many of Fitzgerald’s most celebrated performances, including 1960’s “Live in Berlin,” which contains a high-spirited version of Mack the Knife” in which Fitzgerald forgets the lyrics and improvises through the song for more than four minutes.

“And now Ella . . . and her fellas, we’re making a wreck, what a wreck of ‘Mack the Knife,’ ” she sings at one point.

“You won’t recognize it,” she laughingly sings near the end of the tune, “it’s a surprise hit.”

In fact, the butchered version of “Mack the Knife” spent 14 weeks on the pop charts and garnered Fitzgerald two Grammy Awards for best vocal performance.

Mr. Smith was also at the keyboard for many of Fitzgerald’s classic “Song Book” albums of the 1950s and 1960s, in which she interpreted the works of various composers, including Cole Porter, Duke Ellington, Irving Berlin and the songwriting team of Richard Rodgers and Lorenz Hart, as well as that of George and Ira Gershwin.

In 1960, Mr. Smith and Fitzgerald recorded an album that became known as “The Intimate Ella.” It was little known until after its re-release in the 1990s, when it became recognized as one of the singer’s most emotionally expressive recordings. Jazz critic Will Friedwald called it a “masterpiece.”

On the album’s 13 songs, including such melancholy tunes as “Black Coffee,” “Angel Eyes,” “Misty” and “One for My Baby,” Fitzgerald’s plaintive voice is backed only by Mr. Smith’s nimble, harmonically inventive piano.

“Smith’s accompaniment is faultless,” Nicholson wrote in his 1993 biography of Fitzgerald. “He never gets in Ella’s way with the superfluous or superficial, yet he has the technique and the imagination to complement rather than complicate.”

Paul Thatcher Smith was born April 17, 1922, in San Diego. His father, Lon Smith, had played trumpet in theatrical orchestras before starting a vaudeville act with his wife. They settled in San Diego, where the elder Smith became city editor of the San Diego Union newspaper.

Mr. Smith began piano lessons at age 8, led swing bands in high school and was a full-time musician by his late teens. In 1942, he played in a band led by Ozzie Nelson, who later became a TV star on “The Adventures of Ozzie and Harriet.”

After serving as an Army musician during World War II, Mr. Smith worked with guitarist Les Paul and toured the country with the Andrews Sisters. “It was like working with the Beatles,” he later recalled. “They were mobbed everywhere.”

As the pianist with Dorsey’s band in the late 1940s, the hulking Mr. Smith sometimes lifted the piano off the floor with his knees while pounding out rollicking boogie-woogie tunes.

“One time, the leg fell off while the piano was rocking,” he recalled in 1986. “When I got up to take a bow, I had to hold up the side of the piano with my hand.”

Mr. Smith, who did not smoke or drink, soon tired of life on the road and settled down as a studio musician in California. He was on the staff of NBC and Warner Bros. and worked with such conductors and composers of film scores as Andre Previn, Max Steiner, Dimitri Tiomkin and Alfred Newman. He appeared on recordings with everyone from Jimmy Durante to Dizzy Gillespie and was the music director for TV shows hosted by Steve Allen and Dinah Shore.

After the death of his first wife, Betty, Mr. Smith married singer-pianist Annette Warren in 1958. She dubbed the voice of Ava Gardner in the 1951 film “Show Boat” and the voice of Lucille Ball in two movies, “Sorrowful Jones” (1949) and “Fancy Pants” (1950). She and Mr. Smith recorded an album together and were scheduled to appear this month at a Hollywood jazz club.

In addition to his wife, of Rancho Palos Verdes, Calif., Mr. Smith’s survivors include two children from his first marriage, actress Lauri Johnson and Gary Smith, both of Los Angeles; a son from his second marriage, Paul D. Smith of Riverside, Calif.; eight grandchildren; and two great-grandchildren. A son from his second marriage, Jeffrey Smith, died in 1988.

Mr. Smith had such a fine-tuned musical ear that he could emulate the musical style of any jazz pianist from Fats Waller to Art Tatum to George Shearing, but “I never became deadpan serious about jazz or wanted to sit and play jazz in a club all night,” he said in 1994.

“To me, piano is fun and games,” he added, noting that he often interjected humorous musical asides and jokes in his improvised solos. “I figure one good laugh is worth 1,000 good choruses. And if I get that one laugh, then maybe they’ll listen to the 1,000 choruses.”