Born to wealthy parents, Horace "Hap" Flanigan, a banker, and Aimee (née Magnus) Flanigan, a granddaughter of Adolphus Busch, co-founder of Anheuser-Busch, in Manhattan, Peter Flanigan was raised Catholic. He served as a U.S. Navy carrier pilot during World War II. He graduated summa cum laude from Princeton University and joined the investment firm of Dillon, Read & Company.
Flanigan, a committed Republican, who had supported Nixon over John F. Kennedy in the 1960 U.S. presidential election, was named Nixon's deputy campaign manager in 1968. He served as a presidential assistant until 1972. Such was Flanigan's influence and support for big business that Ralph Nader labeled him as the "mini-president". He resigned from the Nixon administration in June 1974.
Flanigan was nominated as Ambassador Extraordinary and Plenipotentiary (to Spain) by Nixon's successor, President Gerald Ford, however the nomination, which was made on September 17, 1974, was stalled in the Senate and he never received his commission.
Flanigan's first wife, Brigid (née Snow), died in 2006. The couple had five children, one of whom, Sister Louise Marie Flanigan, is a Roman Catholic nun. Flanigan, a widower, married an Austrian national, Dorothea von Oswald, in 2008. The couple had homes in Wildenhag, Oberösterreich, Austria, and in Purchase, New York.
Flanigan died, aged 90, at a hospital in a small town outside Salzburg, Austria, from undisclosed causes.
- Douglas Martin (July 31, 2013). "Peter M. Flanigan, Banker and Nixon Aide, Dies at 90". The New York Times. Retrieved May 27, 2015.
- "Peter Flanigan dies". Fox News. July 31, 2013. Retrieved August 4, 2013.