Farrell was one of the most prolific and influential songwriters, producers, publishers, and music executives of the 1960s and 1970s. To date Farrell's catalogue includes close to 500 songs that he wrote, produced, or published. One of his earliest successes, "Boys" (co-written with Luther Dixon), appeared on the B-side of The Shirelles' number-one 1960 hit "Will You Love Me Tomorrow", and in 1963 was covered by The Beatles for their debut album Please Please Me. Farrell's biggest chart hit – the 1965 US #1 single "Hang on Sloopy" (a reworking of "My Girl Sloopy", co-written with Bert Russell, aka Bert Berns) – remains one of the most performed songs in the history of popular music, according to the RIAA. "Hang on Sloopy" also became the Official Rock Song of the U.S. state of Ohio, and the rock song for Ohio State University. The song is so popular in Columbus, Ohio and on the Ohio State University campus that the song is played at every sports homes game and graduation; the official website of the athletics department is HangOnSloopy.com.
Other Farrell pop hits include The Animals' UK debut single "Baby Let Me Take You Home" (co-written with Bert Russell, #21, 1964) and two big 1964 releases for Jay and the Americans: "Come a Little Bit Closer" (co-written with songwriters Tommy Boyce and Bobby Hart, US #3) and "Let's Lock the Door (And Throw Away the Key)" (with Roy Alfred, US #11 in early 1965). Farrell also co-wrote "Come and Take a Ride in My Boat" (with Jerry Goldstein), slightly reworked in 1967 to provide Every Mother's Son with their signature hit "Come on Down to My Boat" (US #6).
Farrell's Top 40 hit "Look What You've Done" — first recorded in 1966 by the Pozo Seco Singers — appears on Carla Olson's 2013 album Have Harmony, Will Travel as a duet with Rob Waller (of I See Hawks in LA).
In 1966, Farrell wrote the theme song for Gammera the Invincible (aka Gamera), the American cut of the first Gamera film .
Between 1970 and 1973, Farrell hit big with The Partridge Family, co-writing not only "C'mon On, Get Happy" (with Danny Janssen) – the theme to their television series – but nearly 30 songs for their seven studio albums. Partridge Family chart hits co-written by Farrell include "Doesn't Somebody Want to Be Wanted" (with Jim Cretecos and Mike Appel, US #6, 1971) and "I'll Meet You Halfway" (with Gerry Goffin, US #9, 1971). Notable album tracks include "I Can Feel Your Heartbeat" (with Jim Cretecos and Mike Appel), "Brand New Me" (with Eddie Singleton), "I'm Here, You're Here" (with Gerry Goffin), "One Night Stand" (with Paul Anka), "Twenty-Four Hours a Day" (with Danny Janssen), "Love Is All That I Ever Needed" (with David Cassidy), "Hello, Hello" (with Tony Romeo) and "Something New Got Old" (with Bobby Hart).
Recording artists Farrell produced include the Partridge Family (who actually consisted of David Cassidy and Shirley Jones with a team of studio musicians), Elephant's Memory (whose songs "Jungle Gym at the Zoo" and "Old Man Willow" appeared in the movie Midnight Cowboy) and singer Lulu (two 1970s albums).
Farrell went on to found Chelsea Records in 1972.
Farrell was born in 1939 in New York City, New York. In 1965 he married Joan Arthurs, and they had a daughter, named Dawn. Farrell and Arthurs divorced in 1972. He was married to actress/singer Tina Sinatra (daughter of Frank) in 1974, and to actress Pamela Hensley in 1979; both marriages ended in divorce. Farrell was later married to real estate mogul Jean Inman and had two children, named Wesley and Sky. (Sky, a collage artist, died 29 Apr 2014 at age 28.) Farrell died of cancer aged 56 in 1996 in Coconut Grove, Florida.