Delp was born in Danvers, Massachusetts on June 12, 1951. He picked up a guitar at age 13, after seeing the Beatles perform on the Ed Sullivan Show. His brush with the Beatles would lead him to form the Beatles-tribute band Beatlejuice during his off-time from the band Boston. He was a lifelong Bealtes fan.
In 1969, Delp performed in Tom Scholz' band Mother's Milk with guitarist Barry Goudreau and drummer Jim Masdea. Goudreau had introduced Brad to guitarist/keyboardist and recent MIT graduate Tom Scholz, who was looking for a singer to complete a recording of some demos that he had made in his basement. At the time, the band making the demos was made up of Scholz, Delp, and Masdea. The demos eventually became the basis for the music known as Boston. They sent the tapes off to Epic Records, who signed Brad Delp and Tom Scholz in 1976. That same year, the self-titled album, Boston, became the best-selling debut album in history. It sold 17 million records and produced some of the greatest rock standards of all time, including "More Than a Feeling" and "Peace of Mind".
Brad Delp performs with Beatlejuice at Salem High School on March 17, 1995: