Colonel Lawrence Moore Cosgrave was born in Toronto, Ontario, Canada on August 28, 1890. He was a 1912 graduate of the Royal Military College of Canada and subsequently attended McGill University. In World War I he served as a junior artillery officer in the Canadian Army in France.

He served as the Assistant Canadian Government Trade Commissioner in London, England (1922-24); Canadian Trade Commissioner, Wembley, London, England (1924); Shanghai, China (1925-35); Melbourne, Australia (1925-37); and Sydney, Australia (1937-42).

In World War II he was the Canadian Military Attache to Australia, S.W.P.A. but his most notable moment came on September 2, 1945 when he was the Canadian representative who signed the Japanese Instrument of Surrender aboard the USS Missouri (BB-63). He caused little known mishap; Colonel Cosgrave inadvertently placed his signature one line too low on the Japanese copy of the documents. He signed on the line for the French Republic. This set off an unfortunate chain whereby each succeeding signer also signed one line too low on that copy of the documents. The error was "corrected" by General Sutherland who crossed out "French Republic" and wrote in "Dominion of Canada" then made similar corrections for the rest of the document.