Career
Born near Warsaw, he worked in the Grand Duchy of Lithuania and particularly in its capital Vilnius. He was a tutor of Laurynas Gucevičius. Knackfus was influenced by other Polish–German architects of late Baroque (Ephraim Schröger and Szymon Bogumił Zug) and early Neoclassicism (Domenico Merlini and Johann Christian Kammsetzer).
He moved to Vilnius around 1768.
Knackfus served as captain of the Army of Grand Duchy of Lithuania and lectured at military engineering school. Between 1773 and 1777 he taught courses in theory and practical application of architecture at Vilnius University.
He participated in the 1794 Kościuszko Uprising. Fearing persecutions of the Tsarist authorities, he retreated to Suvalkija and largely retired.
Knackfus worked with numerous nobles, including Bishops Ignacy Jakub Massalski and Ignacy Krasicki, Field Hetman Ludwik Tyszkiewicz, voivode Karol Stanisław Radziwiłł, Adam Kazimierz Czartoryski, Grand Marshal Stanisław Lubomirski.