He played as an offensive tackle with the Cleveland Browns from 1954 through 1962 and served as head coach of the Philadelphia Eagles, Baltimore Colts, and Seattle Seahawks.

McCormack came home in 1954 to find that his team had ceased to exist, so he became a free agent and was immediately signed by the Baltimore Colts, a new franchise created the previous year to replace the defunct Yanks/Texans.

He played a key role in helping legendary running back Jim Brown become one of the dominant players in the game, ending his career with six selections to the Pro Bowl.

"[1][2] Also, according to Paul Zimmerman's 1984 book, The New Thinking Man's Guide to Pro Football, Brown also stated that McCormack was the best offensive lineman he ever coached.

McCormack retired from playing in 1962 and began coaching with the first of four consecutive stints as an assistant in the annual College All-Star Game.

In late January 1989, he was abruptly fired by the new Seahawks owner, Ken Behring, who explained the decision was necessary in order to make changes in the financial operations of the team.

[11][12] Later that year, McCormack became a consultant for Jerry Richardson and his ownership group that were seeking to land an NFL expansion team in Charlotte, North Carolina.