1978 Boston Bruins Peter McNab newspaper clipping 28x35cm Sporting News Photo TSN.

McNab is part of a prominent ice hockey family. His father Max McNab was a center who won the Stanley Cup with the Detroit Red Wings in 1950, and later became a coach and general manager. Peter's brother, David, spent 43 seasons as an NHL scout and executive before retiring from his position as the senior vice president of hockey operations for the Anaheim Ducks in May 2021.

Born in Vancouver, British Columbia, Peter McNab spent his early childhood in British Columbia before moving to San Diego, California at age 14, where his father was head coach of the minor-league San Diego Gulls. Peter initially excelled as a baseball player; he entered the University of Denver (DU) on a baseball scholarship and later made the hockey team, becoming an all-WCHA selection in 1973. In the early 1970s NCAA players rarely made it to the National Hockey League, but McNab was drafted by the Buffalo Sabres while playing forward for the DU Pioneers in 1972.