Stepanov was born on 30 August 1893 to a Russian peasant family in the village of Pepel, Soligalichsky Uyezd, Kostroma Governorate.

During World War I, Stepanov was mobilized into the Imperial Russian Army in September 1914 and sent to the Krasnoye Selo Reserve Rifle Battalion of the Petrograd Military District as a private.

From February 1919 he commanded the Communist Regiment of the 2nd Brigade of the 29th Rifle Division of the 3rd Army, leading it on fighting on the Eastern Front against the White forces of Alexander Kolchak in the areas of Tyumen, Ishim, Perm, and Glazov.

[2] In the latter, they fought as part of the southern group of the 15th Army in the area of Lepel, Vileyka, Borisov, Molodechno, and Lida.

From January 1921 he served as chief of the junior advanced courses of the Western Front under the division, and in November became commander of its 37th Rifle Regiment.

[1][2] Having completed the Vystrel course in 1930, Stepanov served as assistant chief of staff of the 3rd Rifle Corps in Ivanovo from December 1931.

Stepanov led the remnants of the division out of the encirclement, escaping with General Ivan Boldin's group.