A graduate of the Royal Military College of Canada, Marius Grinius served in the Canadian Army for 12 years. He joined the Canadian Foreign Service in 1979. Grinius was ambassador to Vietnam from 1997 to 1999), the Republic of Korea from 2004 to 2007 and the Democratic People's Republic of Korea from 2005 to 2007.
He then served as ambassador and permanent representative to the United Nations and the Conference on Disarmament in Geneva from 2007 to 2011. His earlier postings included Bangkok, Brussels (Canadian Delegation to NATO) and Hanoi.
His Ottawa assignments at Foreign Affairs included serving as the desk officer for nuclear arms control and director for Southeast Asia. Later, he had tours in the Privy Council Office (Social Policy, Security and Intelligence) and Western Economic Diversification. In 2011 and 2012, Grinius was seconded to the Department of National Defence as director-general of International Security Policy.
Grinius retired in 2012 after 45 years of service to Canada. He continues to comment on international security, Canadian foreign and defence policy, and Canada’s place in Asia. Currently, he is a fellow at the Canadian Global Affairs Institute, a member of the Advisory Board for the Canadian Centre for Responsibility to Protect and vice-president of the Royal Military Colleges Club of Canada.
He is also a member of the Senate of the 30th Field Regiment, Royal Canadian Artillery, based in Ottawa.