Mosolov attended high school until 1916, and in 1917 worked in the office of the People's Commissioner for State Control. Through this, he personally delivered mail to Vladimir Lenin three times, which had a profound impact on the young Mosolov. At the start of the Bolshevik Revolution, Mosolov volunteered in the Red Army's First Cavalry Regiment and fought on the Polish and Ukrainian fronts. He received the Order of the Red Banner on two occasions. He suffered from post-traumatic stress disorder due to the war and was medically discharged in July 1921. Mosolov entered the Moscow Conservatory, where he studied under Reinhold Glière until 1925; in that year he began composition studies under Nikolai Myaskovsky. He also studied piano under Grigoriy Prokofiev and Konstantin Igmunov. He graduated from the Conservatory in 1925 after presenting his graduation piece, the cantata "Sphynx", based on the Oscar Wilde poem of the same name. That same year, he was granted membership in the Association for Contemporary Music (ACM).