In 1912, Weadick travelled to Calgary, where he met with H.C. McMullen, a livestock agent for the Canadian Pacific Railway. The two of them put together a program for a frontier show. They envisioned a cowboy championship along with a tribute to the Old West. Weadick gained financing from the Big Four: George Lane, owner of the Bar U Ranch; two other wealthy ranchers, Patrick Burns and A. E. Cross; and A. J. McLean, provincial secretary. He staged the first Calgary Stampede September 2–7, 1912, when ranchers and farmers had finished the harvesting and would be free to attend.
Weadick arranged for 200 head of Mexican steers, 200 bucking steers, and wild horses to be brought in from the ranches around Calgary. In order to entice top quality competitors, $20,000 in championship money and world championship titles were offered. The prize money was about four times the closest competition, causing riders from across North America to arrive in the 1912 Stampede. In 1919, Weadick and Calgary Industrial Exhibition manager, E. L. Richardson, agreed to combine the rodeo events with the Calgary Industrial Exhibition and, in 1923, Weadick and Richardson co-founded the Calgary Exhibition and Stampede as an annual event.
Following on the success of the Calgary Stampede, Guy Weadick continued promoting his own personal Old West shows (outside Calgary). He continued running the Stampede for 20 years after its initial creation. His next appearance at the Stampede was to appear in the parade in 1952. He died in 1953.