He began to learn composition at the State Secondary Music School in Warsaw under Sławomir Czarnecki. Later, Kowalski-Banasewicz studied in Marian Borkowski's composition class at the Music Academy in Warsaw, after which he received a diploma with distinction. He furthered his skills at a workshop run by Matias Herman and Marek Chołoniewski at Musikhochschule Stuttgart. In 2002, he participated in the International Seminar of Representatives of Departments of Composition of Higher Music Schools from Central European Countries. He has received a scholarship from the ZAIKS society of authors and composers once (in 2005) and twice from the Minister of Culture and Art (in 1997 and 2006). He is a winner of many composition competitions.
In 2005, the international jury in Zagreb decided to schedule a performance of Bartosz Kowalski-Banasewicz’s Symphony of Circles at the Croatian edition of World Music Days, an annual festival organized by the International Society for Contemporary Music. Additionally, his works have been performed, amongst others, by the Polish Radio Symphony Orchestra, the philharmonic orchestras of Kielce, Katowice and Częstochowa, the Wrocław Chamber Orchestra Leopoldinum, the Croatian Radio Television Symphony Orchestra, the Lviv Chamber Orchestra Leopolis, Schola Cantorum Gedanensis, the Polish Radio Choir in Kraków and the Chamberbrass, Warsaw Brass and Kwartludium ensembles at such festivals as Musica Polonica Nova in Wrocław, Musica Moderna in Łódź, Gaude Mater in Częstochowa, and Warsaw Music Meetings, Audioart, Laboratorium and Uczniowskie Forum Muzyczne in Warsaw.
He also creates music for films. Films with his music have been presented, amongst others, at the Camerimage and Łodzią po Wiśle festivals. He has also created arrangements and orchestrations of classical and popular music works. Amongst his collaborators are Waldemar Malicki (symphonic arrangements for the television programmes What Is This / Co tu jest grane and The Philharmonic of Jokes / Filharmonia Dowcipu) as well as with Alina Mleczko and the Prima Vista quartet (the album La Fiesta).
Since 2005, Bartosz Kowalski-Banasewicz has worked as a lecturer at the Fryderyk Chopin University of Music in Warsaw, where he leads instrumentation and introduction to composition classes. He also collaborates with the juries of the Musica Sacra competition and the composer’s competitions organized at the Józef Elsner State Secondary School in Warsaw.
As an instrumentalist he took part in various events related to improvised music, performing with Krzysztof Knittel, Jerzy Kornowicz, Marek Chołoniewski, Tadeusz Sudnik, and Michał Górczyński. Currently he is a member and co-founder of the band Sonofrenia.
Two works by Kowalski: Contra tempus (2013) and Flautorganix (2015) were co-financed by the Minister of Culture and National Heritage as part of the "Collections" programme – priority "Composers’ orders", implemented by the Institute of Music and Dance. Composition In affecto for violin solo (2015) was an obligatory piece at the 5th Tadeusz Wroński International Competition for violin solo.
He is the author of nearly one hundred compositions, a significant number of which are symphonic, orchestral, choral and chamber works. As an improvising instrumentalist (trumpet, cornet, horn, recorders, piano, guitars, electronic instruments) he takes part in numerous concerts, workshops and happenings. He also creates electronic and film music.
He was awarded the title of composer-resident of the Świętokrzyska Philharmonic (in the 2012/13 season). In 2014, he received the Bronze Gloria Artis Medal awarded by the Minister of Culture and National Heritage.