Lastowski was born on 8 November 1883 in the village of Kalyesnikaw in the Disna uyezd of the Vilna Governorate of the Russian Empire (now Lastovichi, Belarus) into the family of a landless nobleman.

In 1905-1906 he worked as a librarian of a student library in St. Petersburg where he also attended lectures at the Faculty of History without being enrolled at the university.

He attempted to pass examinations to receive a secondary school qualification but, despite good results for the main subjects, failed due to his poor knowledge of the Russian language.

He co-authored The Memorandum of the Representatives of Belarus that formulated the right of the Belarusian people to national and political development and that was presented at an international conference in Lausanne in 1916.

He headed the committee for the 400th Anniversary of Belarusian Book Printing: 1525—1925 as well as the Union for National and State Liberation of Belarus.

The refusal of the Lithuanian government to finance Kryvich and the coup d'état of 17 December 1926 prompted Lastowski to relocate to Soviet Belarus in April 1927.

During an ethnographic expedition organized by Lastowski, the Cross of Saint Euphrosyne, one of the Belarusian national symbols, was found.

On 10 April 1931 Lastowski was sentenced to be exiled for five years to Saratov, where he directed the department of old prints and manuscripts of the university library.

[6] Arrested again on 20 August 1937, Lastowski was convicted as “an agent of the Polish intelligence service and participant of the national-fascist organisation” by the Supreme Military Court of the USSR and executed in Saratov.