Composer and music life organiser. He studied piano with Kazimierz Gierżod in 1983–88, and composition with Włodzimierz Kotoński (1988–94) at the Chopin Academy (now University) of Music in Warsaw. He developed his abilities at workshops for composers conducted by Hanna Kulenty, Henryk Mikołaj Górecki, Michael Nyman, Louis Andriessen, and Tristan Murail, among others. As pianist and composer, he has taken part in such contemporary music festivals as the Warsaw Autumn, the Poznań Music Spring, Musica Polonica Nova, and ISCM World Music Days.

Siwiński has won numerous awards in competitions for works for children, including the International Competition for Jazz Composers in Słupsk (1997) and the “Music and Play” International Competition for Composers in Poznań (1998) as well as “Mikołaj’s Music-Making” H.M. Górecki Music Festival Composers’ Competition in Rydułtowy (2011). He received scholarships from the Minister of Culture and National Heritage, the Capital City of Warsaw, and Society of Authors ZAiKS. 

As a member of MM Group in the 1990s, he co-created projects combining theatre, music, and visual arts. He has collaborated with Eugeniusz Rudnik, Fryderyk Rzewski, Michelangelo Pistoletto, the Viktor Lois / Yin Peet duo, Azorro Group, and many others. His works have been performed by the Polish Radio Orchestra, the Sinfonia Varsovia, Gorzów Philharmonic, OMN New Music Orchestra, Orkest De Ereprijs, and the Forbidden City Chamber Orchestra. He composed the Rzeszów city’s bugle call as well as music for animated films (by Jan Lenica, Daniel Szczechura, Marcin Giżycki, Agnieszka Skolik, Tomasz Kozak, and others), theatrical spectacles and computer games. For many years he has collaborated as pianist and composer with the Children’s Art Centre in Poznań, for which he wrote ca 20 pieces (as part of the Music and Play project). Many of these works actively involve the young audience in the performance. A CD dedicated exclusively to his works was released by the Polish Composers’ Union / POLMIC as part of the Polish Music Today – Portraits of Contemporary Polish Composers series (2013). Since 2017 he has served as artistic director of Warsaw Music Encounters festival of the Polish Composers’ Union’s Warsaw Branch. 

Siwiński’s artistic work revolves around classically conceived music, but often goes beyond that sphere. For instance, 2019 saw the presentation at Warsaw’s Museum of Modern Art of his installation titled Imaginary Chopin featuring an autonomous piano (no performer). In the following year, Siwiński obtained a PhD from the Fryderyk Chopin University of Music for a dissertation concerning the concept of sound installation reacting to weather conditions. 

Selected works: The Misty Eye of the Earthworm for amplified piccolo and two percussion (1989), The Perception of Music is a Complex Process, Not Totally Clear for tape, piano and violin (1990), Notari, E.M. for tape (1992), Pianerecerto for piano and ensemble (1994), Notarimbalo for harpsichord and tape (1994), Dominotales for piano, percussion and children’s audience (1997), Piano Quintet (1998), Hominibus for orchestra (2002), Locomotive for tape to words by Julian Tuwim (2003), Polish Songs for tape (2006), Movement for orchestra (2006), Annalena for baritone and string orchestra, to words by Czesław Miłosz (2011), Chopin Elements for autonomous piano (2012), Sestetto for piano, string quartet and double bass (2013), Variations and Changelings for chamber ensemble, video and children’s audience to words by Małgorzata Kołcz (2013), The Other Side Turned Out to Be for soprano and chamber ensemble to words by Agnieszka Syska (2014), Via caelestis for chamber ensemble (2014), Food Items for woodwind quartet and tape to words by Małgorzata Kołcz (2015), Industrial Music for ensemble of traditional Chinese instruments (2015), HubTub for tuba and ensemble (2016), On Variations and Changelings, educational cartoon for children (2016), Silent Fish, a microopera for children to a libretto by Małgorzata Kołcz (2016), Jeżeli / If for soprano, string quartet and autonomous piano to words by Agnieszka Syska (2016), Ornithologyfor soprano and chamber orchestra to words by Małgorzata Kołcz (2017), Dźwiękosceny / Soundscenes for ladder and various other objects (2017), A Tale from a Shallow Sea for chamber ensemble to a text by Joseph Conrad (2017), Three Coloured Figures for 2 flutes and organ (2018), Imaginary Waltzes for autonomous piano (2019), Aurea, electronic music (2020), Aria for flute, clarinet, violin and cello (2020), Gismondo for two flutes and piano (2020), Trio for flute, violin and piano (2020), I Still Can’t Learn Harmony for tape (2024), There are Tritons on the Fountain, electronic miniature (2024).