He was the keyboard player for New York hard rock band Elf and a founding member of Rainbow.
After his honorable discharge he joined The Elves after the band's original keyboardist, Doug Thaler, was severely injured in a car accident that killed guitarist Nick Pantas.
In the first years of the 1970s, The Elves (after 1972 known simply as Elf) enjoyed minor success as a consistent opening act for Deep Purple.
That connection to Deep Purple opened up the opportunity for Soule (and vocalist Ronnie James Dio) to participate in Roger Glover's 1974 concept album The Butterfly Ball and the Grasshopper's Feast.
Elf had effectively dissolved by the time that album was released as the members hoped to continue with Blackmore.