In 1936 he volunteered to fight in the Spanish Civil War and then moved for educational reasons to Berlin from 1939 to 1941. In 1941 he volunteered to go to Russia to fight in World War II where he contracted frostbite due to the severe cold weather. Olivelli did not want to swear allegiance to the new Italian Social Republic in 1943 and was thus deported to Innsbruck in Austria on 9 September 1943 until he managed to flee and settle in Milan in the evening of 20–21 October. He started to become critical of the Italian regime and believed he could improve it through a more Christian message though later broke from it after seeing the situation with deporting Jewish people as per racial laws and the French invasion. Olivelli became part of the Italian resistance movement in Milan as part of the triangular resistance including Brescia and Cremona branches. He remained in touch with resistance members such as Peppino Pelosi and Carlo Manziana while he was in Brescia. Olivelli worked hard to create the newspaper "Il ribelle" and the first issue published on 5 March 1944 was dedicated to Astolfo Lunardi and Ermanno Margheriti who were both executed not long before. His paper was the underground newspaper for the Green Flames Brigades partisan group. Carlo Bianchi and Claudio Sartori helped him establish the paper in February 1944. Olivelli's codename at this time was "Agostino Gracchi".
