He eventually became the head of the bank's West Coast of S.A. operations centered in Lima, Peru at the age of 28.
[1][2] After returning to school at MIT for two years, in September 1970, Hennessy joined the United States Department of the Treasury as Deputy Assistant Security, responsible for International Economic Development.
[3] On May 2, 1972, he was sworn in as Assistant Secretary for International Affairs, a Presidential appointment requiring the consent and approval of the United States Senate.
In 1989, he became Chairman of Executive Committee and CEO of the merged global bank, Credit Suisse First Boston.
he retired from the Bank to dedicate himself to philanthropic and not-for-profit activities, concentrating on education and programs in developing nations.