He is among the most notable Slavicists of the late 19th and early 20th centuries, and the first to prepare complete monographs on the history of the Polish language and culture.

Brückner was born in Brzeżany (Berezhany) in Galicia, Austrian Empire, to an Austro-Polish family who had moved there from Stryj three generations earlier.

He studied at the German Gymnasium in Lwów (Lemberg) under Omelian Ohonovsky, in Vienna under Franz Miklosich, and in Berlin under Vatroslav Jagić.

In 1876 he received a doctorate at the University of Vienna and in 1878 his habilitation for a study on Slavic settlements around Magdeburg (Die slawischen Aussiedlungen in der Altmark und im Magdeburgischen).

During the First World War, he favored the Central Powers but opposed the Treaty of Brest-Litovsk, which he believed was largely directed against a resurgent Poland, and made deep concessions to the Ukrainians in his native eastern Galicia.