A&M Records first assigned Nick to arrange for Claudine Longet. By November 1967, he had recorded one album and two singles with her. Longet's husband, singer Andy Williams, came to several dates then asked DeCaro to arrange for him.
DeCaro produced Longet's later albums with A&M as well as albums for A&M artists Chris Montez and The Sandpipers. These recordings are often considered the quintessential A&M Records sound. Nick also played on many A&M sessions providing the piano and/or accordion parts on sessions including those for Herb Alpert &the Tijuana Brass and the Baja Marimba Band.
In 1969, DeCaro recorded his own album for A&M Records, Happy Heart. Nick's version was an instrumental which was climbing the Billboard chart. Andy Williams wanted to record it as a vocal and asked DeCaro for an arrangement. Nick's arrangement for Williams is almost identical to his instrumental. Williams' version became a hit in 1969. DeCaro's own album featured his skills as a song writer, arranger, pianist, vocalist and producer.
Nick DeCaro was one of the most prolific arrangers in the music industry from the mid-1960s through the early 1990s. He worked with over 300 artists from Mel Carter to Tori Amos, Elton John to Barbra Streisand, and James Taylor to Dolly Parton. In that time he also returned to arrange songs for a myriad of A&M artists.