This was the last Four Seasons hit to feature bass singer/bassist Nick Massi. The same month "Let's Hang On!" was released, Massi left the group and was temporarily replaced by the band's arranger Charles Calello before Joe Long came in as Massi's full-time replacement.
The popularity of "Let's Hang On!" has been attributed to the inclusion of several devices into the recording: a two-line introduction (sung by lead singer Frankie Valli), the use of two fuzz guitars (one guitarist playing low notes, another playing high notes on a fuzz bass), a chorus loaded with hooks and sung in falsetto, and backing vocals giving counterpoint with Valli's lead vocal. It re-established the group's presence in the Top Ten (of the Hot 100) as The Four Seasons were in a flurry of activity, recording albums both as The Four Seasons and as supporting musicians for Valli's rekindled "solo" career. In the UK, the song was a No. 4 hit for the group.
Billboard described the song as having a "hard- driving dance rhythm."
The single's B-side, "On Broadway Tonight", was the theme of a CBS-TV variety series (1964–1965) hosted by Rudy Vallee.
In 1981, the song was revived by Barry Manilow who hit No. 6 on the U.S. Billboard Adult Contemporary chart and No. 32 on the Hot 100. The single climbed to No. 12 in the United Kingdom and was certified silver, while peaking at No. 4 in Australia, No. 16 in Germany and No. 8 in Ireland.