Jazep Sažyč was born in Haradzieczna (now in Navahrudak district, Hrodna Voblast). He graduated from a Polish gymnasium in Navahrudak. In 1938 he was mobilized into the Polish army where he underwent an officer training course. During the German invasion of Poland Sažyč was commander of a minor military unit. He got wounded and taken by the Germans as a POW. He was later transferred to a hospital in Łódź from where he managed to get to Białystok and later to Navahrudak. He worked as an accountant in a village store and became enlisted as student to the University of Lviv.
However, with Germany attacking the USSR Sažyč was mobilized into the Red Army. He soon deserted and returned to Lviv, where he worked at a shop and supported the Organization of Ukrainian Nationalists.
He then went back to Navahrudak where he joined Belarusian collaborators organizing Belarusian military units. Sažyč served in the local pro-German police. In 1942 he was appointed commandant of the Under Officer School of the Belarusian Self Help. In February 1943 he was given the task to organize a Belarusian railway guard unit in Lida. From July 1943 he taught at an officer school in Minsk.
In July 1944 Sažyč left Belarus to the Western Front in Saarbrücken. The Belarusian undercover government gave him the task to establish contacts with the French Resistance. However, as the Germans got to know about that, Sažyč was immediately transferred to Berlin. In Berlin he was participating in training the Čorny Kot partisan troup and was commandant of the officer school of the 30th Waffen Grenadier Division of the SS (1st Belarussian).
Jazep Sažyč was one of the founders of the Belarusian-American Association in Michigan. From 1953 he was member of the Belarusian People's Republic government in exile; in 1982–1997 he was the government's president.
- (Belarusian) Язэп Сажыч — адзіны з былых старшыняў Рады БНР, які цяпер жыве. Інтэрвію на "Радыё Свабода" - an interview with Jazep Sažyč by Radio Free Europe
- (Belarusian) Памёр былы Старшыня Рады БНР Язэп Сажыч