During the Polish Defensive War of 1939, he was staff officer and commander of the Polish Air Forces in the Army Kraków, then in the Army Lublin. He escaped to Romania, later to France and Great Britain. In London he became the Chief Inspector of the Staff of the Polish Air Forces in Great Britain.
Addressing the language problems of each nation controlling its own trainees during the 1942 Ottawa Air Training Conference (British Commonwealth Air Training Plan) of 14 United Nations countries that was designed to coordinate future air power; Poland's Group Captain Stefan Sznuk explained: Only in one instance does a Polish airman speak this language distinctly and with the proper accent—it is when he speaks to the enemy using the eloquent language of the twelve English-made machine guns of his fighter plane.
Sznuk was the last Polish Army and Air Force attaché in Canada before the Soviet-control of the nation. After the demobilization of the Polish Army he settled down in Canada. He helped over 4,500 Polish veterans emigrate to Canada after World War II and was active in the Polish community as Vice-President of the Canadian Polish Congress.
- Virtuti Militari, Silver Medal
- Polonia Restituta, Commander
- Cross of Valour (Krzyż Walecznych), twice
- Gold Cross of Merit with Swords (Krzyż Zasługi z Mieczami)
- Order of Canada, Officer
- Obituaries of the Ontario Genealogical Society Provincial Index, retrieved on 2008-05-31.
- "Ups & Downs" Time magazine, June 01, 1942, retrieved on 2008-05-31.
- National Army Plaque" Polish Heritage in Canada, retrieved on 2008-05-31.
- Governor General of Canada, retrieved on 2008-05-31.