This unit, titled the 1st York Troop, is generally believed to have started in 1855 under George Taylor Denison III but there are connections to 1822 when G T Denison I formed a troop of cavalry from members of the local militia infantry in York. In 1876 the troop was expanded to a squadron and in 1889 it became a regiment with the addition of C and D Troops. the squadrons were stationed in different places, A and B at York, C at Oak Ridges and D at Markham. The Markham Troop was originally raise in 1810 by Captain Button.
The first action they saw was in the Fenian Raids in 1866. They chased the IRA from Niagara Frontier and the town of Fort Erie, taking many prisoners. Their first battle honour was earned in the North West Rebellion of 1885. By 1897 the regiment was 230 strong and supplied a small contingent to travel to London for the Queen's Diamond Jubilee parade. The GGBG did not serve as such in South Africa in 1900 but many of them volunteered, joining up with other units. Again in 1914 the GGBG supplied volunteers for the CEF as the 4th Canadian Mounted Rifles. Private Holmes of this unit won the VC in October 1917.
In 1937 the regiment amalgamated with the Mississauga Horse. They mechanised in 1941 and fought in World War 2 as the 3rd Armoured Regiment in Italy and in 1943 were employed as a reconnaissance unit. They moved up into Northern Europe with the rest of the Canadian Division. In 1950, fifty of the regiment volunteered to serve in Korea and this has developed over the years with groups serving in the UN peace-keeping force. They remained armoured until a period between 1965 and 1982 when they converted to jeeps. in 1982 they were given Cougar Armoured Cars. The regiment is still the the senior Reserve Armoured Regiment in Canada with Her Majesty the Queen as Colonel-in-Chief since 1988. The Honorary Colonels of the regiment have, since 1867, been the Governor General of Canada.