During World War I, Capello was the commander of several Army corps and led the Italian troops that captured Gorizia (Sixth Battle of the Isonzo).

In June 1917, he reached the apex of his military career when he took command of the Second Army (Italy) and captured the Bainsizza Plateau (Eleventh Battle of the Isonzo).

He was later involved in the planning of an attempt to assassinate Benito Mussolini in 1925 along with Tito Zaniboni (it), for which he was tried and sentenced to thirty years jail in 1927.

Born in Intra (since 1939 a frazione of Virbania) on the shores of Lake Maggiore in relative poverty, before the unification of Italy, Luigi Capello revealed a very strong personality that allowed him to bypass numerous social prejudices.

Promoted to lieutenant general in 1914 he commanded the 25th division (Cagliari) and then with the entry into the World War 1 of Italy, which took place on 24 May 1915, he was assigned to the 3rd Army.

Despite the numerous offensives made during the third and fourth Battles of the Isonzo, the Austrian counteroffensives stymied the best efforts of the Italians.

However, his great ambition helped him to be initially successful during the First World War achieving victory in the Sixth Battle of the Isonzo, with the conquest of the city of Gorizia.

As Commander of the 2nd Army he was able to innovate offensive tactics, and in particular, he supported the creation of the Arditi, so much so as to be the object of dislike by other army officials, who saw in the Arditi, the Praetorians of Capello, and in Capello himself, a general who surrounded himself with mercenaries and the faithful with allegiance to him, creating rivalries that would isolate him at Caporetto.

Capello was placed alongside other Armies by Cadorna in order to repel the Austro-German offensive led by generals Otto von Below and Svetozar Borojević.

The Italian army was unprepared to fight a defensive battle after having conducted all its operations until then in an offensive stance, being unaware of the innovative methods that prevented the troops from getting bogged down in "no man's land".

Germany had developed a fighting technique known as infiltration through the Stosstruppen to counter widely-used trench warfare, thus denying the defenders a continuous line instead of simply overwhelming it through numbers alone.