After gaining his Undergraduate Degree in Economics and Business Administration at Norwich University, Northfield, Vermont, and an MBA from Clark University, Worcester, Massachusetts, Dr. Hennessey worked as a Senior Marketing Analyst for the American Can Company. He then became Marketing Director for Interpace Corporation based in New Jersey. In 1979 he moved into the educational/consulting sector in strategy and marketing. He completed his PhD at New York University and joined Babson College in 1982. He has taught courses on global marketing, marketing strategy, B2B marketing, foundations of entrepreneurship and management, and sales management strategy, and written numerous articles and case studies. He has co-authored four books: Global Marketing Strategies, 6th edition, 2004 (with Jean-Pierre Jeannet), Global Marketing: An Interactive Approach, 3rd edition 2011 (with Kate Gillespie), Global Account Management, 2004 (with Jean-Pierre Jeannet) and How to Write a Marketing Plan, 3rd edition 1996 (with Robert J. Kopp). Dr. Hennessey has had executive and MBA teaching experience in a wide variety of programs at Babson College, Ashridge Management College, IMD, Trinity College Dublin, Erasmus RSM and Helsinki School of Economics and Business Administration as well as in Costa Rica, France, Holland, Germany, Hong Kong, Singapore, Switzerland, Finland, United Kingdom, Ireland and Japan. Participants are from many companies; for example, Electrolux, Unilever, IBM, P&G, ICI, Novartis, BBC, Cable and Wireless, BT, Compaq, Unisys, Philips, and Nokia.

Dr. Hennessey has contributed to custom executive education programs for GTECH, Irving Oil, Home Depot, IBM, Pitney Bowes, SAP, Serono, DSM, Novartis, and others and is the Faculty Director for the Ticona Global Account program.

Hennessey is past president and on the Board of Directors of the Sales and Marketing Executives of Boston. He is a part owner of Winthrop Hill Properties. He holds both a US and Irish passport.