Following the foundation of the Second Polish Republic, Berbecki served in the Polish Army. Peter Leon Berbecki, born on a farm in Kalinowszczyzna in what is now Lublin, was one of four children. After graduating from grammar school, Berbecki enlisted in the army in 1891.
After a short stint as an enlisted man in the 44th Infantry Regiment, Berbecki was sent to a Junkers military school, returning to his regiment in 1893.
After serving as a junior officer, including a stint as quartermaster of his regiment, he left the army in 1901 to study at the Kharkiv Institute of Technology. In early 1903, he was drafted into the Imperial Russian Army as an officer
After the Oath crisis in 1917, he headed the Polish Auxiliary Corps and was the training inspector of the Polnische Wehrmacht. After Poland regained its independence in 1918, he joined the Polish Army.
Promoted to general in June of that year, Berbecki fought in the Polish-Ukrainian War and Polish-Soviet War, commanding the 3rd Polish Legions Division.
During the interwar period, he held various functions in the Polish Army and retired in March 1939. He did not participate in the Polish September Campaign that marked the start of World World War II but was arrested by Nazi Germany and interned along with other Polish officers. He returned to Poland in 1945, and published his memoirs "Pamiętnik generała broni" (Memoires of a General) in 1959.