Born on 24 August 1870 in Saint Petersburg, to an impoverished gentry family with roots in Livonia and Samogitia. His father was an organist at Saint Stanislaus church in St. Petersburg. His mother, Maria Reiter, was a teacher of mixed German and Czech ancestry, and came from Moravia.[1][2] After completing his secondary education he attended Lwow University, where he met his future wife, Wanda Zieleniewska. Both were involved in student politics. He dropped out of his course to follow his political ambitions. Later he briefly attended Prague University, where he met Jan Masaryk. He and Wanda had three daughters: Halszka (born in London) and Wanda and Sofia Aldona (born in Kraków).
Afterwards he concentrated on historical research. He researched linguistics (particularly Slavic languages), ethnography of the Central and Eastern European lands, and history of literature.[2] He would serve as the director of two institutes (Instytut Badania Najnowszej Historii Polski (Institute of Studies of Modern Polish History) in the 1920s and Instytut Badań Narodowościowych (Institute of Nationality Studies) in the 1930s)[3] and editor of the journal Niepodległośc. Supporter of Międzymorzefederation idea, as well as Prometheism, he was also a vocal opponent of polonization, arguing that Ukrainians and Belarusians living in Poland should be allowed to assimilate into Polish society at their will and speed. Author of many works, among them Litwa i Białoruś ("Lithuania and Belarus", 1912), Ukraińska sprawa narodowa w jej rozwoju historycznym ("The Ukrainian National Cause in its Historical Development", 1925), Zarys dziejów PPS ("A Short History of the PPS", 1925), Józef Piłsudski, jakim go znałem ("Józef Piłsudski, as I knew him", 1935).[3]
^ abcdef"Leon Wasilewski's Biography". Archived from the original on January 6, 2009. Retrieved 2007-02-26.{{cite web}}: CS1 maint: bot: original URL status unknown (link) at OŚRODEK MYŚLI POLITYCZNEJ webpage. Last accessed on 25 June 2012