Penhaligon was born on D-Day and brought up in Truro. He was a cousin of actress Susan Penhaligon. He attended Truro School, and then Cornwall Technical College where he studied mechanical engineering. Penhaligon worked for Holman Brothers in Camborne as a research and development engineer working on rock drilling. As an interesting anecdote, he was also a part-time DJ at the Hall for Cornwall where he once encountered 14 year old Roger Taylor, subsequently the Queen drummer, at a musical event that he compered in Truro City Hall during 1964. By 1973 he had qualified as a Chartered Mechanical Engineer; he also took over from his father a sub-post office in Chacewater from 1967 (after his marriage in 1968 to Annette Lidgey, she ran the business). His Liberal activities led to some work in local broadcasting.