The Act Against Slavery was an anti-slavery law passed on July 9, 1793, in the second legislative session of Upper Canada, the colonial division of British North America that would eventually become Ontario. It banned the importation of slaves and mandated that children born henceforth to female slaves would be freed upon reaching the age of 25.

The Province of Upper Canada was a part of British Canada established in 1791 by the Kingdom of Great Britain, to govern the central third of the lands in British North America, formerly part of the Province of Quebec since 1763. Upper Canada included all of modern-day Southern Ontario and all those areas of Northern Ontario in the Pays d'en Haut which had formed part of New France, essentially the watersheds of the Ottawa River or Lakes Huron and Superior, excluding any lands within the watershed of Hudson Bay. The "upper" prefix in the name reflects its geographic position along the Great Lakes, mostly above the headwaters of the Saint Lawrence River, contrasted with Lower Canada to the northeast.