Vincent Anthony Dellaglio was born on July 17, 1928, in San Francisco's North Beach neighborhood. After his mother, Carmella Marcellino, divorced his father, she married Anthony "Tony" Guaraldi, who adopted the boy, and he took the Guaraldi surname. His maternal uncles Joe and Maurice "Muzzy" Marcellino were both active in the San Francisco music scene, and he began piano lessons at age seven. He graduated from Lincoln High School, spent a short time at San Francisco State College, and served as a cook in the U.S. Army during the Korean War.

His first issued recordings, made in 1951 with vibraphonist Cal Tjader's Mambo Trio and released in 1953 on the Fantasy 10-inch LP The Cal Tjader Trio, included "Chopsticks Mambo" and "Lullaby of the Leaves." By mid-1954 he had formed his own trio with guitarist Eddie Duran and bassist Dean Reilly, a group that played regularly at the hungry i in San Francisco and often accompanied the singer Faith Winthrop. In August 1955 a live session at the Black Hawk produced his originals "Ginza" and "Calling Dr. Funk," both issued on Fantasy's sampler Modern Music from San Francisco in 1956, a record that also gave space on other tracks to the pianist Sonny Clark. Fantasy then offered him an exclusive contract and released Vince Guaraldi Trio with Duran and Reilly. In the same period he toured with Woody Herman's Third Herd, and Discogs credits him as the pianist on six tracks of the Herd's Capitol LP Blues Groove, recorded in Chicago in May 1956.

Later in 1956 he rejoined Tjader and became a mainstay of two of the vibraphonist's groups. The first, a straight-ahead quartet, had Al Torre on drums, Eugene Wright on bass and Luis Kant on percussion; the second, formed in 1958, added Latin rhythm with Al McKibbon on bass, Mongo Santamaría on congas and Willie Bobo on drums, and sometimes the reed players Paul Horn and José "Chombo" Silva. He is the pianist on Tjader's 1958 sextet album with Stan Getz and drummer Billy Higgins. His own second album, A Flower Is a Lovesome Thing, was recorded in April 1957 with Duran and Reilly and no drummer and was released that October; it sold poorly, and Fantasy dropped him. He left Tjader's band in early 1959 to concentrate on his own projects, and in April 1961 he appeared on the San Francisco public-television special Trio with the illustrator Don Freeman and the mime Bernard Bragg, in which the three challenged one another to improvise.

The breakthrough came with Jazz Impressions of Black Orpheus, a trio album with bassist Monty Budwig and drummer Colin Bailey, recorded in November 1961 and February 1962 and released in April 1962. It was built on themes from the 1959 film by Antônio Carlos Jobim and Luiz Bonfá, but radio disc jockeys favored Guaraldi's own "Cast Your Fate to the Wind," the intended B-side, over the film material. The record spent 19 weeks on the Top 100 chart, peaking at No. 22, an unusual showing for an instrumental jazz record, and the composition won the 1963 Grammy Award for Best Original Jazz Composition. Asked whether he had sold out, he answered that he felt he had bought in. Fantasy followed with In Person, recorded live at the Trident in Sausalito, and with Vince Guaraldi, Bola Sete and Friends, the first of several records with the Brazilian guitarist Bola Sete, whose duo with Guaraldi lasted from 1963 to 1965. The orchestrated The Latin Side of Vince Guaraldi (1964) used arrangements by Jack Weeks, and on May 21, 1965, he performed a jazz mass he had written on commission for Grace Cathedral in San Francisco, issued as At Grace Cathedral. By then he was receiving only about five percent of his record sales and sued to leave Fantasy; the dispute was dropped in 1967 after Saul Zaentz bought the label, and Guaraldi started his own D & D Records, named for his children David and Dia, whose only release was Vince Guaraldi with the San Francisco Boys Chorus (December 1967).

In 1963 the television producer Lee Mendelson, who was assembling a documentary on the Peanuts cartoonist Charles M. Schulz, heard "Cast Your Fate to the Wind" on the radio and asked Guaraldi to score it. The documentary, A Boy Named Charlie Brown, was never broadcast for lack of a sponsor, but the music came out in 1964 as Jazz Impressions of A Boy Named Charlie Brown and included "Linus and Lucy." Mendelson and Schulz then hired him for A Charlie Brown Christmas, which CBS broadcast in December 1965; his score and the Fantasy soundtrack album added "Christmas Time Is Here" (with words by Mendelson) and "Skating" to arrangements of carols such as "O Tannenbaum," with Fred Marshall on bass and Jerry Granelli on drums. For It's the Great Pumpkin, Charlie Brown (1966) he recorded "Linus and Lucy" with a sextet, and that recording became the definitive version of the franchise's signature theme. He went on to score fifteen Peanuts television specials, the feature film A Boy Named Charlie Brown and the documentary Charlie Brown and Charles Schulz (both 1969).

After years of legal wrangling he signed with Warner Bros.-Seven Arts in 1968 and made Oh, Good Grief!, a set of re-recorded Peanuts themes, followed in 1969 by The Eclectic Vince Guaraldi and Alma-Ville, which moved toward fusion, electric keyboards and more experimental writing. Reviews were mixed, the label did not renew, and he was unable to secure another recording contract. Financially secure from Peanuts royalties, he stayed in Mill Valley, played Northern California clubs, and added Fender Rhodes, Hammond B-3 organ, clavinet, harpsichord and an ARP String Ensemble synthesizer to his palette. His 1970s television scores, including A Charlie Brown Thanksgiving (1973) with Tom Harrell on trumpet, It's a Mystery, Charlie Brown (1974) and You're a Good Sport, Charlie Brown (1975), reflected funk and disco, and in 1974 Eliot Zigmund was among his drummers.

On February 6, 1976, he finished recording sessions for It's Arbor Day, Charlie Brown at Wally Heider Studios in San Francisco, then played the first set that night at Butterfield's Nightclub in Menlo Park. Back in his room at the adjacent Red Cottage Inn between sets, he collapsed, and he was pronounced dead at Stanford Hospital at 11:07 p.m.; the cause was a ruptured abdominal aortic aneurysm, and he was 47. He is buried at Holy Cross Cemetery in Colma. His son David later licensed his father's private tapes for archival albums, including The Charlie Brown Suite & Other Favorites (2003), Oaxaca (2004), North Beach (2006) and Live on the Air (2008). A Charlie Brown Christmas entered the Grammy Hall of Fame in 2007 and the Library of Congress's National Recording Registry in 2012, and in August 2026 the RIAA certified it six-times platinum in the United States, which made it the best-selling jazz album of all time.

Guaraldi was a lyrical, relaxed pianist who favored the trio format. The Black Orpheus album shows his habits: rhythmic clarity, restraint in the bossa nova pieces, and simple, carefully shaped arrangements that highlight the interplay of piano, bass and drums. His Brazilian and Latin interests, which grew out of his years with Tjader and deepened in his work with Bola Sete, helped bring bossa nova into American jazz at the moment Stan Getz and João Gilberto were doing the same. As a writer he could produce a hit melody and a durable standard, and "Linus and Lucy" and "Christmas Time Is Here" are both now jazz-trio staples. The producer and critic Ralph J. Gleason wrote in the liner notes to Jazz Impressions of A Boy Named Charlie Brown that Guaraldi had translated Schulz's sensibility into music while keeping his own voice. Some jazz listeners dismissed the Peanuts scores as commercial or children's music, but All About Jazz critic David Rickert credited them with introducing many listeners to jazz. In the 1970s he moved toward electric keyboards rather than resisting the changes in popular music. The pianists David Benoit and George Winston both credited his music as an influence; Winston recorded the tribute album Linus and Lucy: The Music of Vince Guaraldi (1996) and a second volume in 2010, and Wynton Marsalis recorded a Peanuts tribute, Joe Cool's Blues (1995).