With the re-introduction of race track betting in the United States after World War I, the pair, known popularly as "Catta-Léo", extended their activities to racetracks in Chicago, Jefferson Parish, Louisiana, New Orleans, and others in St. Louis and further afield.

In 1921, along with Dandurand and Louis Letourneau, Cattarinich purchased the Montreal Canadiens of the National Hockey League from the estate of George Kennedy for $11,000.

Although Dandurand was the active partner during their tenure (Cattarinich was known as "The Silent One" and Letourneau sold his stake in 1930), the Canadiens won three Stanley Cups with players such as Howie Morenz, Aurel Joliat, and Georges Vezina.

After a series of losses (amounting to $40,000 for the 1934–35 season alone), Cattarinich and Dandurand sold the club to a syndicate comprising J. Ernest Savard, Maurice Forget, and Louis Gélinas in 1935 for $165,000.

[citation needed] Cattarinich and Dandurand continued their betting business throughout the challenging economic environment of the Great Depression in the 1930s.