The East Division is one of the two regional divisions of the Canadian Football League, its counterpart being the West Division. Although the CFL was not founded until 1958, the East Division and its clubs are descended from earlier leagues.

The four teams in the division are the Toronto Argonauts, Hamilton Tiger-Cats, Montreal Alouettes, and Ottawa Redblacks. Several now-defunct teams have also played in the East Division including two teams from the United States and a large number of teams that have played in Hamilton, Montreal, and Ottawa prior to the current teams from those cities. Additionally, current West Division team, the Winnipeg Blue Bombers have, in the past, spent a number of seasons in the East over three separate stints.

The first organized football club in Canada was the Hamilton Foot Ball Club, a predecessor of the Hamilton Tiger-Cats, in 1869. This was followed by the formation of the Montreal Foot Ball Club in 1872, the Toronto Argonaut Football Club in 1873 and the Ottawa Football Club (the future Ottawa Rough Riders) in 1876.

The first organized competitions were formed in 1883, when the Ontario Rugby Football Union (ORFU) and the Quebec Rugby Football Union (QRFU) were founded. At the time the sport was generally called rugby union or rugby football because its rules were similar to rugby union's, although this would change drastically in the coming decades. The following year, the two provincial unions would form the Canadian Rugby Football Union (CRFU), with Montreal winning the first national championship later that year. The CRFU collapsed before the decade was out, but was re-organized as the Canadian Rugby Union (CRU) in 1891, with Osgoode Hall winning the first CRU championship the following year.

The turn of the 20th century was marked by fundamental changes in the rules of the game. The ORFU was the first competition to adopt the Burnside Rules, which were to revolutionize the Canadian game. The QRFU and CRU initially resisted the changes, but by 1906 the Burnside Rules were in force throughout Ontario and Quebec. Although substantial changes (such as forward passing) were still to come, modern Canadian football would ultimately evolve from John Thrift Meldrum Burnside's code.

W. A. Hewitt was vice-president of the ORFU, and represented the Toronto Argonauts. He sought for ORFU to have uniform rules of play with the CRU, with a preference to use the snap-back system of play used in Ontario. In December 1906, The Gazette reported that a proposal originated from Ottawa for the ORFU and the QRFU to merge, which would allow for higher calibre of play and create rivalries. Hewitt helped organize the meeting which established the IRFU in 1907.

In 1907, in a meeting organized by Hewitt, the ORFU's Hamilton Tigers and Toronto Argonauts joined with the QRFU's Montreal Foot Ball Club and Ottawa Rough Riders (Ottawa had been moving back and forth between the two unions over the past few years) to form an elite competition, the Interprovincial Rugby Football Union (more commonly known as the "Big Four"). Montreal won the first championship that year, taking home the James Dixon Trophy. In 1909 Lord Grey, the governor general of Canada, donated a trophy to be awarded to the CRU champion. The trophy, which became known as the Grey Cup, was not won by an IRFU club until the Hamilton Tigers captured the trophy in 1913. Following the 1915 season, the IRFU suspended competition because of World War I, and did not fully resume until 1920.

From 1925 until 1953, IRFU teams dominated Canadian football, winning 18 of the 26 Grey Cups its clubs contested in that timespan (the IRFU suspended operations from 1942 through 1944 because of World War II). During this period, the calibre of play in the IRFU was recognized as being on par with any league in North America. The Big Four attracted considerable interest in the United States and even had its games televised by the National Broadcasting Company for a time during the 1950s (in fact, these games were more widely available than their NFL counterparts). This interest eventually declined as the National Football League gained prominence and the American Football League rose in popularity. During this time, the IRFU became increasingly professionalized. However, in order to keep up the pretense of amateurism, players were usually paid under the table.