Fennelly has a strong rowing background. He rowed in high school at St. Joseph's in Alameda and continued at Long Beach State before transferring to Cal and rowing one year in the lightweight varsity eight. In 1979, Fennelly became lightweight head coach while serving as rigger apprentice under the legendary Matt Franich. In 1981, he became Cal's full-time rigger upon Franich's retirement.
Fennelly and his wife, Kathleen, live in Alameda with their two sons, Brian and Patrick.