Pietrzak joined the Polish Air Force in 1933, as a member of the 4th Air Regiment where he was flying as a pilot of the Polish 114th Fighter Escadrille Polish 114th Fighter Escadrille and during the Invasion of Poland, he was an instructor in the Central Flying School Centrum Wyszkolenia Lotnictwa nr 1 later flew fighters with the Free French Air Force's GC III/9 squadron.

306 Polish Fighter Squadron as a Sergeant Pilot in August 1941, flying Hawker Hurricanes and Supermarine Spitfires, and was commissioned the following year, eventually becoming a squadron leader.

After starting a second tour with 306 Sqn he joined 315 Polish Fighter Squadron from July 1944 until October 1944, flying P-51 Mustang IIIs.

[1] All his victims were German fighter planes: 3 Messerschmitt Bf 109s and 4.5 Focke-Wulf Fw 190s.

He settled in England after the war, commanding 309 Polish Fighter-Reconnaissance Squadron from July 1945 to January 1947,[2] subsequently leaving the Airforce to become a farmer in Suffolk.