Born in 1978 in Tomaszów Mazowiecki, he graduated with honours in music theory (2005, class of Ryszard Daniel Golianek) and composition (2008, class of Bronisław Kazimierz Przybylski) from the Łódź Academy (now the Bacewicz University) of Music. He also studied electronic music with Krzysztof Knittel. In 2012 he obtained his DMA degree in composition under the supervision of Zygmunt Krauze. He has taken part in masterclasses taught by Marek Chołoniewski and Grażyna Pstrokońska-Nawratil. 

In 2017, his brut represented Polish Radio and won the main prize (selected work) at the International Rostrum of Composers in Palermo (its world premiere was recorded at the inaugural concert of the 57th Warsaw Autumn Festival in 2014). He was nominated for the Coryphaeus of Polish Music as Personality of the Year (2017) and for Polityka’s weekly Passport Award (2018). Zagajewski has won awards in competitions for composers such as BMW Crash! of the Zachęta Contemporary Art Association in Szczecin (two editions), the 48th and 50th Tadeusz Baird Competition for Young Composers, 3rd Grażyna Bacewicz International Composers’ Competition in Łódź, and others. He was twice awarded the Łódź Eureka Prize. In 2014 his Stabat Mater was nominated for the Polonica Nova Award in Wrocław. In 2021 the composer received the Energy of Culture Award. 

His works have been performed at festivals in Belgium, the Netherlands, Turkey, Sweden, Estonia, Italy, France, and Poland (Warsaw Autumn, Musica Polonica Nova, Festival of Premieres – Polish Modern Music, Sacrum Profanum, CODES Festival of Traditional and Avant-Garde Music, Poznań Music Spring, New Music Days, Ad Libitum, Audio Art), as well as at the Cricoteka Centre for the Documentation of the Art of Tadeusz Kantor. In 2016 he was invited to take part in the MusMa European Broadcasting Project. In 2019 he was commissioned by the Südwestrundfunk (SWR) to write a work for the 2020 Donaueschinger Musitage. He has cooperated with artists such as Arkadiusz Jakubik, Dominik Połoński, Agata Zubel, Ewa Liebchen, Łukasz Długosz, Agata Kielar-Długosz, Gośka Isphording, Paulina Wycichowska, Zorka Wollny, Piotr Stasik (their joint Opera about Poland was nominated for the Eagles Polish Film Awards in 2019 in the category of documentary films) as well as ensembles such as Bang on a Can All-Stars, OMN New Music Orchestra, Kwartludium, Kwadrofonik, the Silesian String Quartet, Spółdzielnia Muzyczna Contemporary Ensemble, Hashtag Ensemble, Arte dei Suonatori, the Polish Cello Quartet, Small Instruments, Hańba! and Radical Polish Ansambl. 

His work includes research into rock music, lectures and workshops on 20thand 21st-century music, as well as ear training (he was, among others, a jury member at the mYear Festival of Musical Imagination at Wrocław’s Academy of Music). He is also the author of a cycle of online broadcasts What’s It About? Music Created Today, produced in 2021 for Łódź Philharmonic. Zagajewski is on the faculty of the G. and K. Bacewicz University of Music and the Stanisław Moniuszko Music School Complex, both in Łódź. He is a member of the Polish Composers’ Union and the Warsaw Autumn Repertoire Committee. 

Selected works: Glassmusic-Motet for chamber ensemble and audio track (2007), TR13 for accordion and audio track (2005/14), Birds for accordion, synthesizer and audio track (2008), Leaves for chamber ensemble (2008), unhum for symphony orchestra (2009), Orgadronum for chamber choir (2009), Chronophotographic Scenes, ballet (2011), Oratorio for Orchestra and Warsaw Citizens’ Choir, concerto / performance (with Anna Szwajgier and Zorka Wollny, 2011), Stabat Mater for four mixed choirs and instrumental ensemble (2012), canto for 16 musicians (2012), EC 14 for four PVC tubes (2012), Nature morte for 24 PVC tubes (2013), brut for cello and early music ensemble (2014), Canzona for five cellos (2014), Mechanotexture for chamber ensemble (2015), Woodcuts for chamber ensemble and audio track (2015), La città futurista for 16 amateurs and orchestra (2015), circulatio for accordion, quartertone accordion and orchestra (2015), blockhaus C for sound objects (2015), sculpture (from the way of the cross) for four cellos (2016), Steel-Eyed for two punk rock voices and chamber ensemble (2016), Opera about Poland (2016), Modulor for chamber ensemble (2017), Composition arithmétique for piccolo and monophonic track (2017), Holy God, Holy and Mighty for male voice and chamber orchestra (2018), chanson solide for two marimbas (2019), Constructivist Songs for female voice with percussion and string quartet (2019), LA MER /watch?v=y1RpVZNSw6k for chamber ensemble (2019), ricercar for eight cellos (2019), POWERBIT! for voices, toy pianos and synthesizer, to excerpts from Dorota Masłowska’s Other People (2019), Madrigal Music for six-part choir and six instruments (2019), Concerto for two Flutes and Orchestra (2019), EUR (post cold wave new synth romantic punk) for chamber ensemble (2020), Danses polonaises for two pianos, two synthesizers and audio track (2020), und nur dieser Wind for orchestra (2021), 7 for chamber ensemble (2021), Tired with all these, for restful death I cry for chamber orchestra and video (2022), Danses polonaises for two pianos, two synthesisers, and audio track (2022), [...]! for chamber ensemble and audio playback (2023),  Tree of Life for female voice and chamber ensemble (2023), LOVE LOVE LOVE LOVE for pianist, percussionist, and audio playback (2023), the sun is gone for chamber orchestra (2024), 4 songs to poems by Chava Rosenfarb for male voice and chamber ensemble (2024).