Ernesto Cabruna was born on 2 June 1889 in Tortona, the Kingdom of Italy. His family were merchants. Young Cabruna attended technical school until, on 18 October 1907, he joined the "Carabinieri Reali", Italy's version of military police. The following year, he performed commendably during the 1908 Messina earthquake. On 30 September 1911, he was promoted to "Vice Brigadiere". From April 1912 to May 1913, he was posted to Tripolitania, Libya. He later took part in the occupation of Rhodes.