Hennessey served in the Army in World War II and afterward enjoyed a long academic career as a professor and administrator.
In 1968, he became Dean of Tuck School of Business at Dartmouth.
He accepted the job on the condition that women would be admitted to the business school. He also worked to increase minority enrollment in MBA programs.
In the 1980s, Hennessey served as Provost at the University of Vermont and as the university’s interim president.
He served on numerous non-profit and corporate boards.
In 2006, Hennessey married former Vermont Gov. Madeleine Kunin.
Hennessey died Jan. 11, 2018 at Wake Robin Continuing Care Retirement Community. He was 92.