Romanovsky joined the Volunteer Army upon its creation in December 1917 under Mikhail Alekseyev, serving as head of the military headquarters and later as the army chief of staff. He participated in the Ice March from Rostov to Kuban. He became chief of staff of the Armed Forces of South Russia and in 1919 was promoted to lieutenant general. He became a favorite of Anton Denikin, who had also served under Kornilov, after Denikin became commander of the Volunteer Army. Romanovsky was not a popular figure due to his abrasive personality and his advice to Denikin during the summer of 1919 to not prioritize the siege of Tsaritsyn. He was blamed for the defeats the Volunteer Army subsequently suffered as well as the death of Mikhail Drozdovsky, one of his rivals. In March 1920 the Volunteer Army evacuated from Novorossiysk to the Crimea. On March 16, 1920, after arriving in Theodosia, Romanovsky resigned as chief of staff.