Appel was born in Flushing in Queens, New York, of three-quarters Irish and one-quarter Jewish heritage and was raised Roman Catholic. His father was a successful real estate broker on Long Island. Appel began playing the guitar at age fourteen.
Appel was a guitarist and songwriter for several obscure groups during the 1950s and 1960s. He was a member of The Balloon Farm, and co-wrote their 1967 hit A Question of Temperature. He also was a producer and songwriter for the early metal band Sir Lord Baltimore.
In 1971, Carl 'Tinker' West, the manager of some of Springsteen's early bands - Child, Steel Mill and The Bruce Springsteen Band - referred Springsteen to Appel. Springsteen auditioned for Appel in 1971; Appel told him to come back when he had written more songs. When Springsteen returned in 1972, Appel signed Springsteen to a production contract, and got Springsteen the audition with CBS Records' John H. Hammond that led to CBS's signing Springsteen. He produced Springsteen's first two albums, Greetings from Asbury Park, N.J. and The Wild, the Innocent & the E Street Shuffle, both released in 1973. He also co-produced Springsteen's third and breakthrough album, Born to Run.
Appel gradually fell out of favor with Springsteen during after the recording of Born to Run. Springsteen sought to replace Appel as both manager and record producer with Jon Landau by 1976. A lengthy legal battle between Appel and Springsteen ensued, which was eventually settled out of court. Appel, who was not able to find further success in the industry, subsequently co-wrote the 1992 book Down Thunder Road about his experiences with Springsteen.
Appel is generally credited for his aggressive tactics in getting Springsteen's career started, although his production abilities have often been criticized. However, Appel is also sometimes credited with fostering the looser, more musically adventurous and lyrically romantic approach of Springsteen's first two albums. After Landau took over, Springsteen's work became more tightly focused in musical terms and more political in content.
Appel also co-wrote four songs with Wes Farrell and Jim Crerecos that were recorded by the Partridge Family, including the chart hit "Doesn't Somebody Want to Be Wanted" (US #6, 1971) and the album tracks "Somebody Wants To Love You" (1970), "Rainmaker" (1971) and, in particular, "I Can Feel Your Heartbeat" (1970), which former Partridge Family lead singer David Cassidy occasionally performs in live solo concerts.
- Eliot and Appel, Down Thunder Road, p. 45.
- Heylin, E Street Shuffle, pp. 113-143.
- Eliot, Marc with Appel, Mike. Down Thunder Road. Simon & Schuster, 1992. ISBN 0-671-86898-5.
- Heylin, Clinton, E Street Shuffle: The Glory Days of Bruce Springsteen & The E Street Band, Viking, 2012, ISBN 978-0670-02662-3