The regiment joined the 3rd Brigade, Polish Legions, and in July 1915 was sent to the Eastern Front, to fight against the Imperial Russian Army in the area of Lublin and in Volhynia.

These companies took part in the Battle of Lemberg (1918), and for practical purposes, the headquarters of the regiment were in early February 1919 established in Lwów.

The 4th Legions Infantry Regiment fought in the Polish–Soviet War, after which its headquarters were moved to Kielce, where its reserve battalion had already been stationed.

In mid-March-1939, two NCOs and 68 soldiers, under command of Colonel Leon Pajak, were sent to Westerplatte, Free City of Danzig.

Unable to reach the Polish capital, elements of the regiment managed to get to Modlin, fighting there until the capitulation of the fortress, on September 29.