Jānis Petraškevičs initially studied violin (1985–94) and composition (1994–96, with Ģederts Ramans) at the Emīls Dārziņš Music School in Rīga. He studied composition with Pēteris Plakidis at the Jāzeps Vītols Latvian Academy of Music in Rīga (1996–2003). He continued his compositional sutdies with Sven-David Sandström at the Royal College of Music in Stockholm (1998–99), on a scholarship from the Swedish Institute, and later had postgraduate studies in composition with Ole Lützow-Holm at University of Gothenburg (2004–07). In 2014 he defended his doctoral thesis in musicology at the Jāzeps Vītols Latvian Academy of Music (written under the guidance of Prof. Jeļena Ļebedeva) on a specific notion of multi-dimensionality in music by Stockhausen, Boulez, Ferneyhough, Carter and Ligeti. In addition, he has attended 4th International Academy for New Composition in Schwaz/Tyrol (1996), Darmstadt (1998), Royaumont (2000), Seminar with the Ensemble Ictus (2000), Domaine Forget (2001), the Akademie Schloss Solitude in Stuttgart (2003), and the EarLab in Stresa (2008), under the guidance of professors Boguslaw Schaeffer, Brian Ferneyhough, Fausto Romitelli, Luca Francesconi, Chaya Czernowin, Steven Kazuo Takasugi, and Richard Barrett among others.
Among his honors are First Prize in the competition of the Association of Baltic Academies of Music in Hamburg (2003, for “et la nuit illumina la nuit”, Op. 2), the Carl Larsson Scholarship (2006, for a residency in Fontainebleau), the Fellowship of the Civitella Ranieri Foundation in Umbertide (2013–14), and the Latvian Grand Music Award for the best new composition of the year (2014, for “Darkroom – Ein Phantasiestück für Ensemble”).
His music has been performed in Austria, Belgium, Canada, France, Germany, Italy, Japan, Latvia, Lithuania, the Netherlands, Poland, Sweden, Switzerland, and the UK, including once each at the Biennale di Venezia (2008), the ISCM World Music Days (2008, Vilnius), the concert series Musica Viva in Munich (2012), the festival Warsaw Autumn (2013), the festival Archipel (2015), the festival Ultraschall Berlin (2015), and the Donaueschinger Musiktage (2018).
He has received commissions from a number of important contemporary music institutions. For instance, in 2001 he was selected by the jury of “Reading Panel” for a commission from the Ensemble Intercontemporain – the result was “trop proche/trop loin”, premiered by EIC conducted by Jonathan Nott at the Center Pompidou in Paris; in 2011 he was commissioned to write a new piece for the Ensemble Modern – the result was “Darkroom – Ein Phantasiestück für Ensembl”e (premiered by the Ensemble Modern conducted by Peter Eötvös); in 2014 he was co-commissioned by the Ensemble Modern and Wigmore Hall to write a string octet, thus “gefährlich dünn” was created (premiered by the Ensemble Modern in Wigmore Hall in London); in 2017 he was commissioned by SWR to write an orchestral piece for the final concert of Donaueschinger Musiktage 2018 – subsequently “Dead Wind” was composed (premiered by SWR Symphonieorchester conducted by Peter Rundel). In addition, he has collaborated with Irvine Arditti, Clemens Heil, Carol Robinson, Anu Tali, Ensemble Ictus, ensemble-no, Ensemble SurPlus, Ensemble 32, Ex Novo Ensemble, Gothenburg Symphony Orchestra, Nieuw Ensemble, Nouvel Ensemble Moderne, Ostrobothnian Chamber Orchestra, Phidias Trio Tokyo, Riga Chamber Players, Latvian Radio choir group, and the Latvian National Symphony Orchestra.
His articles on music have been published by two Riga based magazines “Mūzikas Saule” and “Rīgas Laiks” for two decades.
Petraškevičs has lectured on aspects of contemporary music at the Jāzeps Vītols Latvian Academy of Music since 2011, being appointed Senior Lecturer in composition in 2017.