He served in the War of 1812, having been gazetted senior Ensign of the Glengarry Light Infantry on the 6 Feb 1812. In 1813 the young Matheson’s services were so highly appreciated by the military authorities that he was appointed Lieutenant and Pay Master.

He was present at York, Sachett’s Harbour, Cross Roads, Fort George, Lundy’s Lane and Fort Erie. For many years he held the rank of Lietuenant Colonel in the Militia and was Colonel commanding the 1st Military District of Ontario at the time of his death.