After the conclusion of the Polish-Soviet War, Bortnowski traveled to Paris, France, where he began training at the Ecole Superieure de Guerre on November 1, 1920. In September 1922, he graduated and returned to Poland where he received further training at various posts, notably in the staff of the Army Inspectorate in Wilno (modern Vilnius, Lithuania). On August 15, 1924, he was promoted to the rank of Colonel and in October of the following year, he became the commanding officer of the Kutno-based 37th Infantry Regiment. After the May Coup d'État in 1926, he served as the Chief of the 3rd Branch of the General Army Staff for two months starting in November. In February 1928, he was appointed commander of the 26th Infantry Division in Skierniewice. From June 1930, he was transferred to Poznań where he was appointed commander of the 14th Infantry Division. In October 1930, was assigned to the Army Inspectorate in Toruń as an officer. On November 1, 1931, he took command of the Zamość-based 3rd Legions Infantry Division, one of the most prestigious units of the Polish Army.