After mediocre attempts to play football, Guerra became a professional cyclist in 1928, at 26.

In 1930 he won his first Italian National Road Race Championships, the first of five straight wins.

That same year he came second in the Tour de France after Italy's leader, Alfredo Binda, proved in poor form.

His fame was exploited by the Fascist government, which profited from his heroic status.

After retirement, he worked as a team manager for riders such as Hugo Koblet and Charly Gaul.