After a successful high school career, he moved to the University of Pittsburgh to play under coach Jock Sutherland.
During the 1937 Rose Bowl against the Washington Huskies, Daddio contributed significantly in the run game and returned an interception 71 yards in the fourth quarter to secure a victory for the Panthers.
Daddio was selected by the Chicago Cardinals in the fifth round of the 1939 NFL draft, rejoining former Pitt teammate Marshall "Biggie" Goldberg.
Daddio spent over two years with the United States Navy during World War II as a gunnery officer.
[2] Following his stint at Allegheny, Daddio took a position under Stu Holcomb at Purdue University and continued there under Jack Mollenkopf until 1958.