Agostinelli was born to Italian immigrant parents outside of Rochester, New York, and attended the Aquinas Institute. He obtained his BA from St. John Fisher College in 1976 and then his MBA at Columbia University. Agostinelli is a certified public accountant.

In 1995 Agostinelli and Steven Langman started their own firm, the Rhône Group where he has been actively involved in all aspects of the group’s strategy and development since its creation, while maintaining and extending the firm’s broad base of relationships with private families, key corporate decision makers, institutional investors and senior sovereign government officials. He is actively engaged in the sourcing and monitoring of investments across all industries and leads the firm’s investor relations activities. He sits on the supervisory board of Eurazeo.

He is a senior member of the Marine Corps Scholarship Foundation led by the American Patriots Campaign Cabinet, and a senior board director on the American Italian Cancer Foundation. Agostinelli is on the board of trustees of the National Review Institute and the American Veterans Center Agostinelli is known for writing articles in the Wall Street Journal and The Washington Times on various political, economic and social issues. Agostinelli was listed in 1997 as a member of the Bilderberg Group.

Agostinelli is a friend of former French President Nicolas Sarkozy and former Spanish Prime Minister José María Aznar. In 2007 President Sarkozy admitted to Le Monde that Agostinelli, his wife and another family had paid the $60,000 per week fee on a luxury villa for him and his family during his 2006 holiday to the United States. Agostinelli has often been seen jogging with Sarkozy.

Agostinelli is a Director and advisor for many European and American philanthropic and civic institutions. He is a member of the Council on Foreign Relations and a leading supporter of neoconservative causes. He is one of the Founding Members of the Friends of Israel Initiative. He is former Vice-Chairman of the Council for the United States and Italy (CONSIUSA), a member of the Investment Committee of Corporate World Opportunities of BSI Group and a director and advisor to a number of European and U.S. philanthropic and civic institutions. In 2008 Agostinelli provided substantial funding to the presidential campaigns of John McCain and Rudy Giuliani.

In August 2011 Agostinelli gave a speech in the Mahan Reading room at the U.S. Naval War College, where he discussed the potential implications that policy decisions made in response to the 2008 financial crisis could have on U.S. national security Arguing against government decisions to pick winners and losers, he predicted that failure to allow companies to go bankrupt could have pernicious effects on long-term U.S. economic growth, which could lead to unprecedented intrusions into the freedom of American citizens. Agostinelli also warned that deficit spending is giving China increased influence over American affairs, with possible implications for national security. He is also a member of the Reagan Ranch Board of Governors.

A delegation of the Friends of Israel Initiative, which included Agostinelli, met with President Shimon Peres at Beit HaNassi in Jerusalem in July 2011. The delegation included former Spanish Prime Minister José Aznar, former US Ambassador to the United Nations John R. Bolton, and Nobel Peace Prize laureate Lord David Trimble. The president held a working meeting with the group and presented an overview of the situation in Israel and the region at large. Agostinelli stated: “Israel is a fundamentally important part of the Western world. It is a democracy under fire, and we must be resolute in defence of its legitimacy.”

Agostinelli is based between New York City and Palm Beach, he maintains additional homes in London and Paris, all of which are interior designed by Jacques Grange. In 2014 Agostinelli reportedly purchased the first landmarked estate in Palm Beach known as “La Loma” built by Gustav Maass and John Volk, which was on the market for $14.5 million through Sotheby’s International Realty and sold for $12 million. According to the Sunday Times Rich List 2015, Agostinelli is ‘building a home in Henley-on-Thames’. In 2017 The Sunday Times reported that Agostinelli recently spent £25 million on a home in South Kensington, London. He counts Nicolas Sarkozy, George W. Bush, Jeb Bush and José María Aznar as close friends. He has also invested £60 million in WeWork.