A graduate of the Royal Military College of Canada, Marius Grinius served in the Canadian Army for 12 years, including in the United Kingdom and West Germany. Marius joined the Canadian Foreign Service in 1979. He was Ambassador to Vietnam (1997-99), to the Republic of Korea (2004-07) and to the Democratic People's Republic of Korea (concurrent 2005-07). He then served as Ambassador and Permanent Representative to the United Nations and the Conference on Disarmament in Geneva (2007-11). His earlier postings included Bangkok twice, Brussels (Canadian Delegation to NATO) and Hanoi. 

Marius’ Ottawa assignments at Foreign Affairs included desk officer for nuclear arms control and Director for Southeast Asia. Later he had two tours in the Privy Council Office (Social Policy Development and Security and Intelligence). He also did a tour in the Department of Western Economic Diversification. In 2011-12 Marius was seconded to the Department of National Defence as Director-General International Security Policy. 

Marius retired in 2012 after 45 years of service to Canada. He continues to write and give presentations related to 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 R2P (Responsibility to Protect) and Vice-President of the Royal Military Colleges Club of Canada.