Thys won the 1913 Tour de France in front of Gustave Garrigou of France and Marcel Buysse of Belgium.
Thys also won the 1914 Tour de France in in front of fellow countrymen Henri Pelissier and Jean Alavoine.
In addition, Thys won the 1920 Tour de France in front of Belgians Hector Heusghem and Firmin Lambot.
The Tour de France was not held from 1915 through 1918 due to World War I.
In the one-day races, Thys was second in the 1919 Paris-Roubaix Classic behind Henri Pelissier of France.
Thys also won both the Tour of Lombardy Classic in 1917.