With the outbreak of the Great War, Bortnowski interrupted his higher studies and joined the Polish Legions where he commanded a platoon in the ranks of the 1st Infantry Regiment.

From his release from Beniaminów to October 1918, Bortnowski acted as commander of the Kraków branch of the Polish Military Organisation.

On 31 October 1918, Lieutenant Colonel Bortnowski joined the Polish Army which was reborn after Poland had regained her independence at the conclusion of World War I.

After the conclusion of the Polish–Soviet War, Bortnowski traveled to Paris, France, where he began training at the École Supérieure de Guerre on 1 November 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 15 August 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.

[2] 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 the autumn of 1938, Bortnowski took command of the Independent Operational Group Silesia which took participation in the occupation of Czechoslovak territory resulting from the Munich Agreement.

Next, the combined forces of the Pomeranian and Poznań Armies took part in the Battle of the Bzura, a counter-offensive devised by Kutrzeba.

Initially in Great Britain, where he was one of the founders of the Józef Piłsudski Institute in London, he eventually emigrated to the United States in 1954.

He supposedly regretted that he had not "during the first days of the war – during the Battle of Tuchola Forest, put a bullet through his (Bortnowski's) head and assumed command".

It is alleged that as a result of the bombardment during the Battle of the Bzura, as well as the break-through towards the Modlin Fortress, Bołtuć may have suffered from a nervous breakdown.

Bołtuć attributed to Bortnowski the series of disastrous events of September 1939 that eventually resulted in Nazi Germany's and the Soviet Union's occupation of Poland.