Victoria Day (French: Fête de la Reine, lit. 'Celebration of the Queen') is a federal Canadian public holiday observed on the last Monday preceding May 25 to honour Queen Victoria, who is known as the "Mother of Confederation". The holiday has existed in Canada since at least 1845, originally on Victoria's natural birthday, May 24. It falls on the Monday between the 18th and the 24th (inclusive) and, so, is always the penultimate Monday of May (May 19 in 2025 and May 18 in 2026). Victoria Day is a federal statutory holiday, as well as a holiday in six of Canada's ten provinces and all three of its territories. The holiday has always been a distinctly Canadian observance and continues to be celebrated across the country. It is informally considered the start of the summer season in Canada.

The same date is also, since 1952, recognized as the currently reigning Canadian monarch's official birthday (though, previously, that event had been marked in Canada typically on each monarch's actual birthday). In Quebec, before 2003, the Monday preceding May 25 of each year was unofficially the Fête de Dollard, a commemoration of Adam Dollard des Ormeaux, initiated in the 1920s to coincide with Victoria Day. In 2003, provincial legislation officially created National Patriots' Day (French: Journée nationale des Patriotes) on the same date.

Royal birthdays for members of French and British royal families were commemorated in various parts of Canada since the 17th century. These were ad hoc commemorations, rather than holidays enshrined in law. Early commemorations were typically marked by an official ceremony, such as a levee and military review, banquets, and sporting events. Several different days were used to celebrate a sovereign's birthday. The birth date for George III, June 4, was observed from the late 18th century to decades after his death in 1820. Until the mid-19th century, the monarch's birthday was more of a military occasion than a civil celebration, as it was the day when able-bodied men in the colony assembled into their militia units for their compulsory military training, as well as attended reviews and celebrations in commemoration of the monarch.

Shortly after the Canadas were united into the Province of Canada, the Parliament sought to create a new public holiday that would form common ground between English and French Canadians, helping them transcend their religious and cultural differences. The birthday of Queen Victoria was selected to be transformed into a public holiday, as it was a date that appealed to both English and French Canadians. At the time, loyalty to the Crown was seen as a key trait that distinguished Canada from the United States and the monarchy was viewed as a "guarantor of minority rights" in the colony. The Queen's birthday was officially designated as a public holiday by legislation passed in 1845, transforming the date from a military event to a civilian holiday and making it Canada's now-oldest official holiday.

On Victoria's 35th birthday, in 1854, some 5,000 residents of Canada West gathered in front of Government House (near present-day King and Simcoe Streets in Toronto) to "give cheers to their queen". An example of a typical 19th-century celebration of the Queen's birthday took place on May 24, 1866, in Omemee, also in Canada West: The town mounted a day-long fête, including pre-dawn serenades, picnics, athletic competitions, a display of illuminations, a torch-light procession, and a gun salute at midnight. By Canadian Confederation in 1867, Victoria Day celebrations were held in communities in Ontario and Quebec and would later spread to other parts of the country as it expanded.

Even as the inhabitants of the Red River Colony, in the then-British territory of Rupert's Land, resisted Canadian expansion, clashing with agents of Canada's government in 1869 and 1870 as Canada negotiated the purchase of Rupert's Land from Britain, the Red River Colony's provisional government celebrated Victoria's birthday with a show of skill at the militia's drill.

The day had become a "patriotic holiday" by the 1890s. Amid the Victoria's Diamond Jubilee in 1897, the Senate passed a bill that aimed to fix the Queen's birthday in perpetuity as a holiday in her honour. It was sent to the House of Commons, where it languished as a private member's bill without government support. It was not until after Victoria's death in May 1901 that the Queen's Birthday was made a perpetual statutory holiday by which to remember the late Queen, who was deemed the "Mother of Confederation". Some members of Parliament proposed the holiday keep the name Queen's Birthday, while others proposed changing it to Queen Victoria Day or Victorian Empire Day. The name Victoria Day was selected by Prime Minister Wilfrid Laurier, who wanted to avoid an imperialist name that would antagonize French Canadians. The Crown-in-Council, the following year, designated May 24 as the official birthday of King Edward VII.

Victoria Day served as the King's official birthday until 1910, when King George V acceded to the throne. From then until 1952, Victoria Day only honoured Queen Victoria's contribution to Canadian Confederation, with the reigning monarch's official birthday typically observed in June, instead. However, for King George VI's tour of Canada in 1939, the King's official birthday was changed to May 20, so he could be present for official festivities; still, Victoria Day was also treated as a day to celebrate the King's birthday.