Stepanov supported the Bolsheviks after the October Revolution, and continued to serve in the Workers' and Peasants' Red Navy. Between February and May 1918 he participated in the Ice Cruise of the Baltic Fleet, the evacuation of the fleet's ships from Revel and Helsinki to Kronstadt. From September 1918 to March 1919 Stepanov commanded the minelayer "Sheksna", and from March 1919 to March 1920, he served as Chief of Staff of the . In March 1920 he was briefly acting commander of the flotilla, and saw action against the White Finns on Lake Onega. In May 1920 he became chief of staff of the Black Sea Fleet's marine detachment, temporarily serving as chief of the West Black Sea coast defence sector, between Ochakov and Odessa, from June to August 1921. From August 1921 to December 1924 Stepanov was Chief of the Operational Directorate of the Naval Staff, and from December 1924 to October 1925 Chief of Staff of the Black Sea Fleet.