He was a volunteer in Col. Fitzgibbon's rifle company, prior to the Rebellion of 1837, and attended every drill until it was disbanded. On the Rebellion breaking out, he served for a while as one of the guard protecting the Commercial Bank; and was in the force that marched out to Gallows Hill and dispersed Mackenzie's followers. A few days after, he went as lieutenant in a company of militia, forming part of the column commanded by Col. Sir A. MacNab, to the village of Scotland, in the County of Brant, and from thence to Navy Island, where he served throughout the whole siege. He was one of the three officers who carried the information to Sir Allan, which led to the cutting out and destruction of the steamer _Caroline_. In November, 1838, he was appointed lieutenant in his father's troop of cavalry, now the Governor-General's Body Guard; and then just placed under the command of his brother, the late Col. Richard L. Denison. He served for six months in active service that winter, and put in a course of drill for some weeks with the King's Dragoon Guards, at Niagara. He was alderman for St. Patrick's ward for some years. In 1849, when Lord Elgin, in Toronto, opened the session of Parliament, Col. G. T. Denison escorted His Excellency to and from the Parliament House. The following account of this affair is copied from the "Historical Record of the Governor-General's Body Guard," by Capt. F. C. Denison:-- "In Montreal, during the riots that followed the passage of the Rebellion Losses bill, the troops of cavalry that had been on regular service for over ten years, forgot their discipline, forgot their duty to their Queen's representative, forgot their _esprit de corps_, and sat on their horses and laughed while the mob were engaged in pelting Lord Elgin with eggs. This Toronto troop acted differently, and established a name then for obedience to orders, that should be looked back to with pride by every man who ever serves in its ranks. Unquestionably there was a great deal politically to tempt them from their duty, and to lead them to remain inactive if nothing worse. But their sense of duty to their Queen, through her representative, was so strong, that they turned out, taking the Governor-General safely to and from the Parliament Buildings, much against the will of a noisy, turbulent crowd. This was an excellent proof of what _esprit de corps_ will do, and of the good state the troop must have been in. His Excellency was so pleased with the loyalty, discipline and general conduct of the escort on this occasion, that he sent orders to the officer commanding, to dismount his men, and bring them into the drawing room. By His Excellency's request, Captain Denison presented each man individually to him, and he shook hands with them all, thanking them personally for their services. They were then invited to sit down to a handsome