He fought as a volunteer in the First World War, reaching the rank of captain in the Arditi and earning a Bronze Medal of Military Valor.

[6] In 1940 he volunteered for the Greco-Italian War, commanding a battalion of the 83rd Infantry Regiment with the rank of major (later promoted to lieutenant colonel) and receiving another Bronze Medal.

[8] On 28 August 1943, after the fall of the Fascist regime, he was recalled into Army service and given command of a battalion of the 215th Coastal Division, which he disbanded after the armistice of Cassibile of 8 September 1943.

[16][17] On 26 April 1945, as the Italian Social Republic collapsed with the Allies advancing beyond the Po and the partisans taking control of the major northern Italian cities, Tarchi tried to flee to Switzerland along with Guido Buffarini Guidi, former Minister of the Interior of the Italian Social Republic (in the previous days, Tarchi and Buffarini Guidi had tried to persuade Mussolini to cross the Swiss border), but they were arrested near Porlezza by the Guardia di Finanza, which had placed itself at the orders of the National Liberation Committee.

[22] In the 1960s, he was elected city councilor of Milan with the Italian Social Movement, and in 1967 he published a book of political reflections, entitled Teste dure.