He started his career as an aide to Democratic Senator William Proxmire of Wisconsin, who headed the Senate Banking Committee. He had campaigned for the Lyndon B. Johnson-Hubert Humphrey ticket in the presidential election of 1964, where he first met J. Bruce Llewellyn. In 2008, he donated US$114,550 to Democratic candidates, including David Price, Mark Begich, Charles B. Rangel, Carl Levin, Dan Maffei, Byron Dorgan, Nita Lowey, Mark Warner, Kirsten Gillibrand, Frank Lautenberg, Jay Rockefeller, Mark Pryor, Max Baucus, Nancy Pelosi, Chris Dodd, Bill Richardson, Joe Biden, Hillary Clinton, and Barack Obama.
In 1994 and 1995, he served as a member of the Moynihan Commission on Government Secrecy, and in 1996 as Senior Advisor to the Aspin–Brown Commission. He was a member of the President's Intelligence Advisory Board under President Bill Clinton.
In 2000, he served as Vice-Chairman of the Report of the National Commission on Terrorism, also known as the Bremer Commission. According to Sonnenberg, twenty out of twenty-five recommendations from the report made it to the USA Patriot Act. He has claimed the September 11 attacks could have been prevented if all the recommendations had been implemented.
In 2002, he chaired the Task Force Report No. 40 of the Council on Foreign Relations called Terrorist Financing. In 2003, he served as co-Chairman of the National Commission for the Review of the Research and Development Programs for the Intelligence Community. He has also served as an official American observer at elections in Latin America, including El Salvador. He serves on the Board of Advisors of the Chertoff Group, headed by Michael Chertoff.
Finance and law
He has worked for the defunct financial firm Bear Stearns and the law firms Greenberg Traurig and Manatt, Phelps & Phillips. He currently serves as Senior International Advisor at J.P. Morgan Chase. He sits on the Board of Directors of the Harlem Educational Activities Fund.
- Panay Gupte, 'Maurice Sonnenberg: A Concerned Optimist', in The New York Sun, March 23, 2005 
- Steven Aftergood, 'The Sonnenberg Phenomenon', on Federation of American Scientists blog, November 18th, 2010 
- Benjamin Weiser, 'The Last Days of Bruce Llewellyn', in The New York Times, May 7, 2010 
- 2008 Political contributions
- Clinton archives biography
- Loch K. Johnson, Strategic Intelligence: Understanding the Hidden Side of Government, Praeger Publishers, 2006, p. 253 
- M.S. Grolier, Perspectives on Intelligence, Nova Biomedical, 2002, p. 7 
- Clinton archives
- Loch K. Johnson, The Threat on the Horizon: An Inside Account of America's Search for Security after the Cold War, Oxford University Press, 2011, p. 420 
- Terrorist Financing
- Roy Gutman, How We Missed the Story: Osama Bin Laden, the Taliban, and the Hijacking of Afghanistan, Washington, D.C.: United States Institute of Peace Press, 2008, p. 255 
- Paul E. Sperry, Infiltration: how Muslim spies and subversives have penetrated Washington, Nashville, Tennessee: Thomas Nelson, 2005, p. 138 
- National Commission for the Review of the Research and Development Programs appointment
- Congressional Record
- Chertoff Group Board of Advisors
- Chertoff Group appointment
- HEAF Board of Directors