He began racing professionally in 1940 but his early career was limited to Switzerland by the Nazi occupation elsewhere.

He was multiple Swiss national champion and a three time winner of the Tour de Suisse.

Kübler's most successful years in international racing were 1950–1952, when the classics had resumed after the Second World War.

[4] His biggest rival, Hugo Koblet, won the following year and as of 2021 they are the only riders from Switzerland to win the Tour.

[5] Kübler was a high-spirited and impulsive rider sometimes given to strategically unwise attacks, out of exuberance and competitive drive.