He was born in Savona on 18 July 1882, the son of Antonio Mercalli and Gabriella Marchesi Massimino, and after enlisting in the Royal Italian Army he participated in the Italo-Turkish war, where he was awarded a Bronze Medal of Military Valor for having distinguished himself during the battle of Psitos, in Rhodes, on May 16, 1912.

He was at the head of the IV Corps, part of the 4th Army of General Alfredo Guzzoni, when Italy entered the Second World War.

He was then replaced by General Carlo Spatocco at the head of the IV Corps, and between 29 November 1941 and 30 September 1942 he held the position of commander-in-chief of the Italian Armed Forces in Albania, with headquarters in Tirana.

[2][5][6][7][8][9][4] On 5 September 1943, after the British landings in Calabria, Mercalli studied a counterattack aimed at repelling the Allied forces and maintain possession of the Aspromonte, but this could not be carried out due to the order issued by Field Marshal Albert Kesselring to the 15th Panzergrenadier Division to withdraw to Castrovillari in order to counter an expected allied landing in the Gulf of Taranto.

After the proclamation of the Armistice of Cassibile three days later, Mercalli remained loyal to the royalist government and made contact with the advancing Allied forces in Calabria; from December 1943 he became president of the Supreme Military Tribunal for liberated territories, and from July 1944, he was attached to the Ministry of War, remaining there until July 18, 1955, when he was discharged from the Army.