Commercial success and songwriting development
The line-up of Brigati on lead vocals, Cavaliere on organ, Cornish on guitar and Danelli on drums was present in the Young Rascals' debut single, the Pam Sawyer/Lori Burton "I Ain't Gonna Eat Out My Heart Anymore", which was performed in their first television performance on the program Hullabaloo on February 24, 1966. But the track reached only No. 23 in Canada and did not reach the Top 40 of the US chart. After the modest success of "Eat Out My Heart Anymore", Cavaliere assumed the lead vocals on their subsequent records, starting with its follow-up "Good Lovin'", originally recorded by Lemme B. Good and The Olympics in 1965, with the same arrangement and different lyrics from the original. Ironically, David Brigati had been the lead singer of the Starliters, but never had any hits; once Joey Dee had a hit with "The Peppermint Twist" he took over the lead vocals. History repeated itself when Felix replaced Eddie as the Rascals' lead singer. They performed "Good Lovin'" on The Ed Sullivan Show. The Young Rascals version became their first Canada/USA No. 1. Shortly after, their eponymous debut album was released, mostly composed of garage rock renditions of folk rock ("Just a Little" and "Like a Rolling Stone"), and soul tunes ("Mustang Sally" and "In the Midnight Hour"), with only one original, the Cavaliere/Cornish penned "Do You Feel It". The Young Rascals reached No. 15 on the Billboard Top LPs chart and No. 10 in Cashbox. The album was certified Gold by the RIAA.
From there the songwriting partnership between Felix Cavaliere and Eddie Brigati began to flourish. Cavaliere wrote the music and themes, and Brigati, the verses with the former's help. Their second album, December 1966's Collections, had four Cavaliere/Brigati songs and two Cornish originals in its eleven tracks. Follow-ups to their number one record, "You Better Run"–later covered by Pat Benatar in 1980 – and "Come On Up", did not do as well as their predecessor (peaking at No. 20 and No. 43, respectively). The band made their UK debut on December 1, 1966, at The Scotch of St. James club in London. Paul McCartney attended the concert and was so excited by the band that he also attended their show the following night, held at the Blaises Club.
In the meantime, Cavaliere began dating high school student Adrienne Bechurri. Their relationship inspired him to write several songs in 1967, including Top 20 "I've Been Lonely Too Long" and Top 10's "How Can I Be Sure", and "Groovin'", their second No. 1. "Groovin'", having its laid-back sound and an Afro-Cuban groove, found some resistance with Atlantic's head Jerry Wexler; "I've Been Lonely Too Long" and the jazz-influenced "A Girl Like You" talked about the advantages of a relationship against loneliness, but the introspective "How Can I Be Sure", with Brigati's lead vocals, expressed the doubts about love, like Cavaliere's conflicting feelings about Bechurri. All these songs were included on the Groovin' album, which had the majority of the tracks penned by Cavaliere/Brigati. Bruce Eder, writing for AllMusic, rates Groovin' as the Rascals' best, noting the record's soulful core and innovative use of jazz and Latin instrumental arrangements.
Groovin' marked the first time that the Young Rascals used outside musicians, bringing some important collaborators like Chuck Rainey, Hubert Laws, and David Brigati to augment their sound. Particularly, David Brigati also helped his brother's band in arranging vocal harmonies and singing background on many Rascals records. The band, especially Cavaliere, wanted to depart from their "singles act" label to be more like an "albums act", something that would become common to more artists at the late 1960s. The album Once Upon a Dream, released at 1968, is an example of this change, because it was the first Rascals album designed from conception as an album, rather than as a vehicle to package their singles (eight of Groovin''s eleven songs had been released as single A- or B-sides, most in advance of the album). Once Upon a Dream also incorporated Indian music in its sound, adding Eastern instruments like sitar, tamboura, and tabla. David Brigati made a special appearance on the album, singing lead on the title track. The psychedelic "It's Wonderful" was released before the album, but its different style from their earlier singles hindered its sales, and the single only reached No. 20. The album's song "My Hawaii" became a top-of-the-charts hit in Hawaii.
The band billed themselves as the Young Rascals for the last time with the single release of "It's Wonderful"; from that point on they were known as simply The Rascals. Their first single release as the Rascals was 1968's optimistic "A Beautiful Morning", which reached No. 3. Internationally, the band was exceptionally popular in Canada, where "A Girl Like You", "How Can I Be Sure?" and "A Beautiful Morning" all reached No. 1. But they struggled in the UK, where they only twice reached the top 75, with "Groovin'" (No. 8) and "A Girl Like You" (No. 35).
Time Peace: The Rascals' Greatest Hits, released in mid-1968, topped the U.S. album chart and became the group's best-selling album. In the same year, "People Got to Be Free", a horn-punctuated plea for racial tolerance (the band was known for refusing to tour on segregated bills) just months after the assassination of Martin Luther King Jr. and of Robert F. Kennedy, became their third and final U.S. No. 1 single, and their sixth and final Canadian No. 1. It was also their final U.S. Top Ten hit, although they remained a Canadian top 10 act for the next few years.
In 1969, the Rascals released the double album Freedom Suite. An album with one LP dedicated to "conventional" songs and another to instrumentals, it should have been the band's definitive change to produce more ambitious albums, according to Richie Unterberger. But Freedom Suite was their last Top 40 album, peaking at No. 17. Brigati's songwriting contributions were diminished on this album, in favor of Cavaliere's solo compositions, as well his vocals, singing lead only on two songs on Freedom Suite. Brigati's participation declined even more in later albums.