After the outbreak of World War I, Sinigaglia volunteered into the Royal Italian Army and was assigned to the 2nd Regiment Granatieri di Sardegna Mechanized Brigade. After a period of training he took part in the offensive against Monte Sabotino and Monte Podgora. In 1916 he was promoted to lieutenant and served in the Battle of Asiago. He later took part in the Sixth Battle of the Isonzo at Monte San Michele and Gorizia. On 9 August 1916, Sinigaglia led his men in an attack on Hill 4 of Monte San Michele. He was hit by Austrian fire and was transported the hospital at San Vito al Torre where he died the next day.