McCarthy was a three-year starter at quarterback who rewrote large sections of the record book as a Holy Cross signal caller in the early 1960s. At the time of his graduation, he held school records for rushing touchdowns in a season (12 in 1962), yards of total offense in a game (304 at Boston College in 1960), yards of total offense in a season (1,721 in 1962) and yards of total offense in a career (4,534). McCarthy also scored 25 career touchdowns and graduated as the second leading modern-day scorer in New England history with 176 career points.
He won the O'Melia Award as a sophomore after leading the Crusaders to a 16-12 victory over Boston College, and took home the prestigious Bulger Lowe Award as a junior as the best collegiate player in New England. McCarthy placed second in the nation in total offense (1,509 yards) as a junior in 1961, then came in seventh as a senior in 1962 (1,721 yards). He also still holds NCAA records for single-season two-point conversions (six in 1960), career two-point conversions (13) and career two-point conversion passes (19).
Following his senior season, he was selected to play in the Senior Bowl in Mobile, Ala. After graduation, McCarthy spent five years in the Marines and is a Vietnam veteran. He then began a career as the director of alumni relations at Holy Cross.