Michael Joseph Stack III (born June 5, 1963) is an American attorney and former politician who served as the 33rd lieutenant governor of Pennsylvania from 2015 to 2019.

[2] Stack attended the Judge Advocate General's Legal Center and School at the University of Virginia and entered the United States Army Judge Advocate General's Corps.

[6][7] While serving as lieutenant governor, Stack had a high-profile falling out with governor Tom Wolf, owing in part to Stack's alleged mistreatment of staff and a difference in management styles with Wolf.

[8] On May 15, 2018, Stack lost the state Democratic primary for lieutenant governor to Braddock Mayor John Fetterman,[9] placing fourth overall.

[10] Stack is the only lieutenant governor of Pennsylvania to lose his renomination bid.