[2] O'Neill was born in Santa Monica, California, and spent much of his early life in Asia and Europe.
He graduated from Princeton University with a Bachelor of Arts Degree in European Civilization in 1969 and served as a lieutenant in the Marines between 1969 and 1971.
He moved to First Interstate Capital Markets in 1984 and returned to Continental in 1989 to manage its mergers and acquisitions advisory business, becoming CFO in 1992.
[4][5] In 1999 he became chief executive of Barclays Bank but resigned after two months because he had developed an arrhythmic heartbeat.
[6] The New York Times later identified O'Neill as the driving force behind a months-long secret effort to oust Pandit, which culminated in a surprise ultimatum to Pandit stating that he must resign immediately, resign at the end of the year, or be fired.