 Tadeusz Pełczyński was the son of Ksawery Pełczyński, a Sanniki sugar-mill technician, and Maria, "née" Liczbińska, a teacher, and was a great-grandson of Michał Pełczyński, a general in the Army of Congress Poland.Pełczyński began school in Łęczyca.In 1905 he participated in a school strike connected with Polish efforts to win independence from the Russian Empire.