Valli was born Francis Castelluccio in Newark, NJ, on May 3, 1934. (The date of 1937 often shown for his birth is erroneous and was propagated to make him seem younger.) His father, Anthony Castelluccio, was a barber; his mother, Maria Castelluccio, was an Italian immigrant. He became interested in singing early, finding particular inspiration when he saw Frank Sinatra perform at the Paramount Theater in New York City in the 1940s. His early mentor was Texas Jean Valley, who took him to auditions, and as a result he adopted the same last name, although he tried several different spellings before settling on Valli. In 1953, he was signed to the Corona subsidiary of Mercury Records, which released his debut single, a revival of the Georgie Jessel hit "My Mother's Eyes," with a credit to Frankie Valley. This was followed in 1954 by "Forgive and Forget," issued on Mercury itself and credited to Frankie Valley & the Travelers. Neither record sold. Valli then hooked up with the Variety Trio, which became the Variatones and, when they were signed to RCA Victor Records, the Four Lovers. The Four Lovers managed one chart single, "You're the Apple of My Eye," in 1956, and continued to release records into 1957. In July 1958, Valli returned to solo recording with "I Go Ape," released by OKeh Records and credited to Frankie Tyler. The same year, the Romans released "Come Si Bella" on Cindy Records, with "Real (This Is Real)," credited to Frankie Valli & the Romans, on the B-side. Frankie Vally & the Travelers put out "It May Be Wrong" on Decca in October 1959, and "Hal Miller & the Rays," another pseudonym, were responsible for "An Angel Cried" on Topic Records in 1960, the same year that "the Village Voices" (Valli and the rest of the former Four Lovers again) had "Too Young" on Topix Records. Topix also issued two singles by "Billy Dixon & the Topics," "I Am All Alone" and "Lost Lullaby," in 1961. None of them succeeded.

Neither did a revival of the Bell Sisters hit "Bermuda," issued by Gone Records in late 1961 by the Four Seasons, a name Valli and his group had taken from a New Jersey bowling alley. By this point, the group included singer/guitarist Tommy DeVito, who had been in the Four Lovers, singer/bassist Nick Massi, and singer/songwriter/keyboard player Bob Gaudio. The group had been signed to a personal services contract by songwriter/producer Bob Crewe, who used them as backup singers and musicians. On Crewe's instructions, Gaudio wrote a song deliberately intended to showcase Valli's multi-octave vocal range, in particular his ability to glide smoothly from a high tenor to a powerful falsetto. The song was "Sherry," which Crewe sold to Vee-Jay Records. Released in July 1962, it took off and hit number one, the first of three consecutive chart-toppers for the group. From the start, the Four Seasons (or the 4 Seasons, as they were numerically billed on their records) emphasized the talents of their lead singer; album covers and record labels carried the legend, "Featuring the 'Sound' of Frankie Valli." That sound, of course, was the falsetto.

The Four Seasons scored five Top 40 hits and three chart albums in 1963, then had seven Top 40 hits and six chart albums in 1964. The success continued in 1965 with four more Top 40 hits and three more chart albums. That year also marked Valli's return to solo work, although, unlike most members of groups who strike out on their own, he determined to do so while still remaining the lead singer of the Four Seasons. Indeed, he continued to use Gaudio and Crewe as his writer/producers. Valli solo recordings were distinguished from Four Seasons group recordings in the sense that the group did not provide backup and harmony vocals. Also, Valli sang in his natural voice, not a falsetto, and the material hewed to more of a middle-of-the-road pop style. Signing to the Smash Records subsidiary of Mercury Records (while the Four Seasons recorded for Mercury's Philips division), Valli launched his new solo career in October 1965 with the single "The Sun Ain't Gonna Shine (Anymore)," written by Crewe and Gaudio, and produced by Crewe. Perhaps because there were also two Four Seasons singles in the marketplace at the same time, "Let's Hang On!," and the pseudonymous novelty "Don't Think Twice," credited to the Wonder Who?, both of which became hits, "The Sun Ain't Gonna Shine (Anymore)" was a failure for Valli. (Some measure of the record's real worth came within six months, when the Walker Brothers covered the song in an identical arrangement and were rewarded with a Top 20 hit in the U.S. and a number one in the U.K.)

Undaunted, Valli returned to solo work in December 1965 with a second Smash single, "(You're Gonna) Hurt Yourself," again from the Crewe/Gaudio songwriting team. This time, he scored; the record peaked in the Top 40 in February 1966. The Four Seasons' success continued in 1966, with another four Top 40 hits and three chart albums. Valli's third solo single, Crewe and Gaudio's "You're Ready Now," was a flop upon release in April 1966, barely making the Cash Box chart and missing the Billboard Hot 100 entirely, but like "The Sun Ain't Gonna Shine (Anymore)," it proved to be a song with an afterlife. Taken up by British fans of Northern soul years later, it was re-released in the U.K. in 1970 and became a Top 20 hit there. Valli moved over to Philips for his next solo single, Crewe and Gaudio's "The Proud One," released in October 1966, which made the singles charts but was not a big hit. Thus, after four singles, Valli didn't have much to show for his career apart from the Four Seasons.

Believing that his record label was not giving his solo work sufficient attention, Valli hired independent promotion to push his next release, and everything changed with his fifth single, "Can't Take My Eyes Off You." A romantic ballad that built to a brassy climax, it took off upon release in April 1967, peaking at number two in Billboard on July 22, 1967. (In Cash Box, it went all the way to number one.) Philips responded by releasing Valli's first solo album, which was called, naturally, Frankie Valli: Solo. (Actually, the full title was The 4 Seasons Present Frankie Valli Solo, and in the trick photograph on the cover, the members of the group, including Valli, were shown holding up a platform on which Valli stood.) Technically, the album was a compilation in the sense that seven of its ten tracks had been released previously on singles; only Valli's revivals of the standards "My Funny Valentine" and "Secret Love" and a remake of his first record, "My Mother's Eyes," were newly recorded. But since his previous singles hadn't been nearly so successful, the material was not so familiar. The LP reached the Top 40.

Although Valli did not leave the Four Seasons, either to launch his solo career or once he had scored his first big solo hit with "Can't Take My Eyes Off You," it may be argued that his solo work had a deleterious effect on the group's career. The year 1967 marked a crucial transition in popular music, as the Beatles' Sgt. Pepper's Lonely Hearts Club Band, released in June, and the San Francisco Summer of Love, with acid rock group like Jefferson Airplane and the Grateful Dead, changed styles drastically. Recording artists were focusing as much or more on albums as they were on singles. The Four Seasons' brain trust -- Valli, Gaudio, and Crewe -- were savvy observers of the pop scene, and they listened carefully to hit records by others to adapt popular sounds to their own discs. With the exception of Gaudio, however, they were older than their contemporaries on the pop scene. (Valli, for example, was actually a year older than Elvis Presley, though he claimed to be two years younger, which, even if true, still would have made him three years older than the oldest of the Beatles.) Their sensibility was more in line with traditional show business in the Frank Sinatra mold than the new hippie counterculture. And with the success of "Can't Take My Eyes Off You," they may have been more interested in pushing Valli as a new Sinatra than the Four Seasons as a psychedelic act. Specifically, at a time when recording artists everywhere were scrambling to record their own Sgt. Pepper's, the Four Seasons kept pumping out singles instead.

Several of those singles were successful. The Four Seasons enjoyed three more Top 40 hits in 1967 -- but their only album release for the year was called New Gold Hits. In fact, the disc technically constituted a regular album, not a compilation, since a majority of its tracks were previously unreleased. But it certainly wasn't a concept album on the order of Sgt. Pepper's. Meanwhile, Valli's next solo single was Crewe and Gaudio's "I Make a Fool of Myself," released in August 1967. It peaked in the Top 20 in October. "To Give (The Reason I Live)," another Crewe/Gaudio composition, followed in December, peaking in the Top 40 in February 1968. The Four Seasons' hitmaking machinery went awry in 1968 after a Top 40 revival of the Shirelles' "Will You Love Me Tomorrow" at the start of the year. Still unable to come up with an album, they stumbled with follow-up singles "Saturday's Father" and "Electric Stories," which missed the Top 40. Meanwhile, however, work was proceeding on a Valli solo album, his first prepared as such, and it appeared in July under the title Timeless. This easy listening effort mixed some new original material with Valli's takes on recent standards such as "By the Time I Get to Phoenix," "Sunny," and "Eleanor Rigby." It proved to be only a modest seller.

The Four Seasons finally entered the concept album sweepstakes in January 1969 with The Genuine Imitation Life Gazette, but it flopped. In May 1969, Valli released what was actually his first solo single in a year and a half, Raymond Bloodworth and L. Russell Brown's "The Girl I'll Never Know (Angels Never Fly This Low)." It reached the Top 40 in Cash Box, but not in Billboard. Nearly a year went by until the release of another Valli single, a revival of the Fortunes hit "You've Got Your Troubles (I've Got Mine)" that did not chart, in April 1970. The same month, the new Four Seasons single, "Patch of Blue," which did chart briefly, had a new artist credit: "Frankie Valli & the 4 Seasons." The two acts were also billed together -- as "Frankie Valli/The 4 Seasons" -- the next month on the LP release Half & Half, which interspersed Valli solo and Four Seasons group recordings, one after another, throughout the disc.

Neither Valli nor the Four Seasons charted again on Philips Records, where they stayed through the end of 1970. With the departure of Tommy DeVito in early 1971 and Gaudio in 1972 (he merely retired from the stage act, continuing to share ownership of the group name with Valli and to write and produce for the group), the Four Seasons formally became known as Frankie Valli & the Four Seasons. After a one-off single with the U.K. branch of Warner Bros. Records in 1971, both Valli as a solo and Valli & the Four Seasons as a group signed to Motown Records, where their recordings were to be issued on the newly formed MoWest subsidiary. The first product of this association was Valli's February 1972 single "Love Isn't Here (Like It Used to Be)," which did not chart, launching a frustrating two years in which a series of Valli and Valli & the Four Seasons releases were unsuccessful. Valli and Gaudio finally split with Motown in 1974, taking with them one unreleased track, a solo ballad called "My Eyes Adored You," written by Crewe and Kenny Nolan. Valli then signed strictly as a solo act to the newly formed Private Stock Records label, which released "My Eyes Adored You" as a single in October 1974. The result was a major comeback. The track hit number one on the Hot 100 on March 22, 1975. Valli's debut album for Private Stock, Closeup, released that month, got halfway up the Top 100. The disco-ish follow-up single "Swearin' to God" (written by Crewe and Denny Randell), released in April, peaked in the Top Ten in July.

Meanwhile, Valli and Gaudio managed to get a new contract for the Four Seasons with Mike Curb's Curb Records, then distributed by Warner Bros. At this point, after many personnel changes in what was essentially Valli's backup band, the group consisted of drummer/singer Gerry Polci, guitarist John Paiva, bassist/singer Don Ciccone, and keyboardist Lee Shapiro. Their label debut, billed as the Four Seasons, not Frankie Valli & the Four Seasons, was the single "Who Loves You," released in July 1975. It peaked in the Top Five in November. In October, Motown took advantage of Valli's renewed popularity by releasing Inside You, an album consisting mostly of previously unreleased tracks; it sold modestly. The same month, Valli released his next new single, a cover of the Ruby & the Romantics hit "Our Day Will Come." It peaked just outside the Top Ten in December, and the subsequent Our Day Will Come LP was a chart item the same month, giving Valli three chart LPs in a single year. Actually, it was four if you counted the Four Seasons LP Who Loves You, released in November (and six counting the compilations Frankie Valli Gold and The Four Seasons Story). But Who Loves You revealed that Valli was taking a less dominant role in the group than he had in the '60s. The next Four Seasons single, drawn from the album, was "December, 1963 (Oh, What a Night)," issued in December, and Gerry Polci's voice was more prominent than Valli's on it. The track became a major hit, topping the charts, which seemed to bode well for a plan by which Valli and Gaudio, while retaining ownership of the group's name (with Gaudio continuing to write and produce the records) would spin the Four Seasons off as a separate act from Valli, who would go on solo completely, once and for all.

Valli charted with three solo singles in 1976: "Fallen Angel" (which made the Top 40), "We're All Alone" (the Boz Scaggs song), and "Boomerang" (which made the Cash Box list, but not the Billboard one). Valli, his LP release for the year, did not sell. Meanwhile, "Silver Star," another single drawn from the Who Loves You album, became the Four Seasons' first Top 40 hit not to feature a Valli lead vocal. Valli's 1977 album, Lady Put the Light Out, did not sell, nor did the singles he released that year. Nevertheless, he took even more of a back seat on the next Four Seasons album, Helicon, which barely scraped into the charts, and following a farewell tour, he announced his departure from the group in the fall. His first single of 1978, "I Could Have Loved You," was another failure, but then he was chosen to sing the newly written title song for the film adaptation of the Broadway hit Grease, written by Barry Gibb of the Bee Gees. Valli sang "Grease" over the opening credits, and his single, released by RSO Records, was a massive hit, peaking at number one in August and going platinum. (Valli also had a part in another movie musical released in the summer of 1978, Sgt. Pepper's Lonely Hearts Club Band.) Signing to Warner/Curb, he released a new album, Frankie Valli...Is the Word, that month, and it made the lower reaches of the charts.

Valli made the Easy Listening chart with his single "Save Me, Save Me" in November 1978 and the pop charts with "Fancy Dancer" in January 1979. Unbeknownst to fans, however, he was struggling to overcome otosclerosis, a rare disease that threatened to leave him deaf. Ultimately, he underwent three operations before correcting the problem. Meanwhile, the Four Seasons, far from flourishing on their own, foundered and broke up in 1979. Valli began recording for MCA Records in 1980, cutting the album Heaven Above Me and a minor chart single, "Where Did We Go Wrong," that was a duet with Chris Forde. But he also agreed to join a Four Seasons reunion tour that began in the spring of 1980 without him, once he had recovered from his last operation. He was back in time to be with the band for the recording of a live album in July. That album, a double-LP called Reunited Live, appeared on Warner Bros. Records in early 1981, and it marked a permanent re-establishment of a group again known as Frankie Valli & the Four Seasons. Even so, Valli made the occasional single without the group, notably "Can't Say No to You" with Cheryl Ladd for Capitol Records in 1982 and "American Pop" with the Manhattan Transfer for Atlantic Records in 1983. He and the Four Seasons teamed up with the Beach Boys for a single called "East Meets West," released on FBI Records, a label he and Gaudio had formed, in 1984. In 1985, MCA/Curb released a new Frankie Valli & the Four Seasons studio album, Streetfighter. For the most part, Valli and the group's releases from the early '80s on were repackagings of their hits, with solo and group recordings mixed together and the discs credited to Frankie Valli & the Four Seasons. In addition to touring, Valli found time for occasional acting stints, appearing in the feature films Dirty Laundry (1987), Eternity (1989), Modern Love (1990), and Opposite Corners (1995), and in TV movies. Valli was inducted into the Rock & Roll Hall of Fame as a member of the Four Seasons in 1990. In 1992, Curb released another new studio album, Hope + Glory, this time credited simply to Four Seasons.

Valli continued to tour extensively. He had a continuing role as a mobster on the acclaimed cable TV series The Sopranos (that is, until his character got whacked). In the mid-2000s, he and Gaudio developed a "jukebox" musical featuring Valli and Four Seasons hits. Unlike ABBA's Mamma Mia!, which integrated the group's songs into a fictional script, however, Jersey Boys was nothing less than a stage biography of the Four Seasons. It opened on Broadway on November 6, 2005, to critical acclaim and went on to win the Tony Award for best musical. The show brought increased exposure to the group, which in turn led to renewed interest in Valli, who signed a new recording contract with Universal Motown and, on October 2, 2007, released his first solo album in 27 years, Romancing the '60s, a collection of covers of '60s hits he'd never recorded before.