Born in Warsaw in 1954, he studied composition with Włodzi mierz Kotoński and double bass with Alfred Wieczorek and  Andrzej Mysiński, at the Chopin Academy of Music in Warsaw.  In 1986, he received the Witold Lutosławski Scholarship, which  enabled him to continue his composition studies in 1986–87  with Isang Yun in West Berlin and Klaus Huber in Freiburg im  Breisgau. As a double bassist, he has toured widely in Europe,  Asia, and the United States, performing the contemporary solo  repertoire. He also makes improvised music, playing with Mud  Cavaliers and Laterna. In 1995, his A Very True Story for tape  won a prize in the EAR radio competition in Budapest; in 1999,  his Concerto à rebours for violin and orchestra was recommended  at the International Rostrum of Composers in Paris.

Wielecki has also devoted himself to promoting contemporary  music and arts education. On Polish Radio he presented his own  programmes for children and young people: Something Out of  Nothing, Sound Graces, and Contemporary Music Hits. He worked  with the Children’s Art Centre in Poznań and the Association of  Culture and Education in Warsaw. He chaired the Artistic Committee of the 1992 ISCM World Music Days in Warsaw. In 2004,  he was invited to teach at the Darmstadt International Summer  Courses for New Music.

His commissioners have included the Darmstadt Courses, Warsaw Autumn, Poznań Philharmonic, Polish Radio and the Polish Radio Orchestra, Klangspuren Schwaz, Ad Libitum Warsaw,  Hiroshima Symphony Association, Klangforum Wien, Ensemble  OMN, the Karol Szymanowski Music Society, Forbidden City  Chamber Orchestra in Beijing, Plural Ensemble, Orkest De Ereprijs, Ensemble intercontemporain, Music Workshop, the Silesian String Quartet, Kwartludium, TwoGether Duo, the Polish  National Radio Symphony Orchestra, and many other ensembles  and institutions.

From 1999 to 2016, he was director of the Warsaw Autumn International Festival of Contemporary Music. In 2024–25, he served  as music director of the National Theatre in Warsaw.

2026 marks another stage in his cooperation with the Dutch Orkest De Ereprijs. In March, as senior composer, he gave one-toone tutorials to participants in the orchestra’s Young Composers Meeting in Apeldoorn. On 6 June, the Andriessen Festival  in Arnhem saw the world premiere of his Rhetorical Music for  orchestra with soprano, commissioned by Orkest De Ereprijs and  written for Ereprijs Xtra’s symphonic forces.

The recording of his radio drama How should I put it… was nominated for this year’s Fryderyk Award in the Album of the Year –  Contemporary Music category.

Selected works: Six Miniatures for piano (1979), Tango for  clarinet, trombone, piano, and cello (1980), Opened Series I–IV  for double bass (1982–85), Trio for Violin, Double Bass and Piano – Music for the White Valley (1985), Collage-Tango for piano  (1985), Ductus for small string orchestra and harpsichord  (1986), Numerous Branches of Ramified Plaits for clarinet, piano  and cello (1988), Gestures of Soul for organ, accordion, synthesizer, guitar and percussion (1989), Counting Game for four  speaking musicians (1990), The Thread is Spinning… I for cello  (1991), The Thread is Spinning… II for violin (1992), Beggar Ballad for chamber ensemble (1994), Egocentric Poem for amplified  piano and tape (1994–95), Collage-Tango for chamber orchestra (1995), Id for large orchestra (1996), Study of Gesture II for  piano (1997), Concerto à rebours for violin and orchestra (1998),  Crest for chamber orchestra (1981, rev. for orchestra, 2000), Surfaces for symphony orchestra (2002), Time of Stones for amplified double bass and chamber orchestra (2002), String Quartet  (2004), Whisper of the Semitones for double bass and chamber  ensemble (2004), Shoals for symphony orchestra (2005), Necessity and Chance for string quartet and electronic media (2006),  The Valley of Dry Water for chamber orchestra (2007), Piano  Concerto (2008–9), The Thread is Spinning… IV for double bass  and chamber ensemble (2012), The Little Shoemaker and the False  King, a chamber opera for children and adults (2013), Reading  for orchestra (2014), From the Depths I Sing… for wind instruments, piano, guitar and percussion (1993, rev. 2014), A Study  of Gesture IV for string trio and percussion (2015), Wobbliness.  Dynamistatic Composition II for traditional Chinese instruments  (2015), Gentle Swaying. A Dramatised Form for bass clarinet, violin, tape and an informal group of performers (2012–16), Multiple  Image for chamber ensemble and ticking clocks (2016), Words for  piano and ukulele (2016–17), Sound Pranks for sounds, gestures,  and facial expressions, for children and adults (2017), I Sound  Therefore I Am for accordion and cello (2017), Ungraspability for  piano, harp, and percussion (2018), There Was Once an Old Man  and an Old Woman… for speaking double bassist (2019), Vibrations for accordion and orchestra (2019), Anamnesis for symphony orchestra and electronics (2019), Continuations for accordion (2020), How should I put it… , a radio drama for soprano,  two actors, chamber orchestra and electronics (2021), Varia for  percussion and piano (2023), Poster for chamber orchestra and  sampler (2023), …And They Are Free of Original Sin for string  quartet and a harp with hemp strings (2025), Rhetorical Music  for orchestra with soprano (2026).