It was built in 1840–1841 to replace Toronto's original Fort York at the mouth of Garrison Creek as the primary military base for the settlement.

[1] Two 18-pounder guns were placed on the lakeshore just to the east of the future fort site, known as the Western Battery, to protect the approach to the harbour.

To finance the new fort, Lieutenant Governor Colborne approved the sale of some of the military reserve lands in 1833.

Approval was given in 1839 by Lieutenant-Governor Bond Head to build a new fort to accommodate 300 soldiers, based on an 1833 plan drawn up by Lieutenant-Colonel Gustavus Nicolls.

[8] In the 1860s, the space at the new fort was insufficient and The 13th Hussars were quartered in the nearby Crystal Palace exhibition building.

In 1870, the British Army withdrew from the Fort, with the property turned over to the Canadian Militia, the official turnover happening in 1871.

The fort became mostly vacant, used only by a few military families for living quarters and the Ontario Rifle Association for training and exhibitions.

In 1874, the new North-West Mounted Police used the fort to train a group of recruits for deployment in Manitoba.

[16] Later in the 1890s, troops of the Dragoons and the RCR from the fort helped to police the Yukon Gold Rush.

Troops of the Dragoons and RCR also joined British forces fighting in South Africa in the Second Boer War.

As the CNE grew in size every year, the City of Toronto sought to take more and more of the Military Reserve.

The City promised to preserve the Old Fort and the graveyard and to allow all military activities on the property to continue until replacement facilities were built.

The barracks were used as a receiving station for the internment of German, Austro-Hungarian, and Turkish citizens, considered "enemy aliens".

Before the war was over, many were pardoned and released upon the signing of pledges of loyalty to the laws of Canada and to report regularly to police stations.

In 1998, the Ukrainian community of Toronto erected a plaque at the Officers' Quarters to memorialize the internment.

The new Princes' Boulevard necessitated the demolition of some of the Barracks' buildings, including some stables and the riding school.

A compromise was made and new stables were built and the military offered the use of the Coliseum and Livestock arenas.

[23] During World War II, the fort and many of the nearby exhibition buildings were again used by Canadian troops prior to being sent overseas.

The CNE Camp was used as a demobilization centre for returning troops at the end of the war[27] before closing on June 1, 1946.

[30] The Government of Canada contributed 50% of the cost to convert the buildings (there were 31 at the time) for emergency civilian housing.

The Archaeological and Historic Sites Board of Ontario erected a plaque commemorating the fort on November 11, 1963, near the former Officers' Quarters.

[37] In 2004, plans were developed to build a hotel and conference centre on the fort site, north of the Quarters.

[39] An entrance pavilion to the hotel is a steel lattice structure that approximates the shape of the enlisted men's barracks.

[40] Regiments from the British Army and the Canadian militia that were garrisoned at the fort include: The two-storey Officers' Quarters is designed in the Georgian style with influences of English Palladianism.

[41] In 2009, City Council approved the development of a hotel on the property, just to the east of the fort's site.