He was awarded the Bavarian Maximilian Order for Science and Art in 2018 and the Bach Prize of the Free and Hanseatic City of Hamburg in 2023.

[a][4] He later studied composition with Hans Werner Henze, Wilfried Hiller in Munich and Heiner Goebbels, Wolfgang Rihm in Karlsruhe.

[5] He studied as a clarinetist at the Hochschule für Musik und Theater München with Gerhard Starke (1986–1997, Meisterklassendiplom 1997)[6] and at the Juilliard School in New York City with Charles Neidich (1994–1995, Advanced Certificate 1995).

[11][12] He has premiered several clarinet concerti dedicated to him: in 1999 through "musica viva", he played Music for Clarinet and Orchestra by Wolfgang Rihm;[2] in 2006 with the WDR Symphony Orchestra, Cantus by Aribert Reimann;[2] and in 2015 "über" by Mark Andre at the Donaueschingen Festival.

[17][18][19] His chamber music partners include Daniel Barenboim, Tabea Zimmermann, András Schiff, Kim Kashkashian, Hélène Grimaud, Denis Kozhukhin and Mitsuko Uchida.

[37] Widmann premiered Am Anfang[38] by Anselm Kiefer in July 2009 as part of the 20th anniversary of the Opéra Bastille, in which he acted as composer, clarinetist and made his debut as conductor.

[41] Widmann's Free Pieces for Ensemble: Number X is used in Sophie Fiennes's documentary Over Your Cities Grass Will Grow (2010), about the postwar German artist Anselm Kiefer.

[42] His sister[2] Carolin Widmann premiered his études IV-VI for violin (2004–2010) at the Wittener Tage für neue Kammermusik on 23 April 2010.

[56] Widmann's oratorio ARCHE had its world premiere on 13 January 2017 on the occasion of the opening festivities of the Elbphilharmonie in Hamburg.

[57][58][59] A concert with Widmann, Daniel Barenboim, and Anna Prohaska opened the Pierre Boulez Saal in Berlin on 4 March 2017.

[60][61] On 27 January 2018, Widmann and the Hagen Quartet performed his Clarinet Quintet, as part of a European tour, at Amsterdam's Muziekgebouw aan het IJ.

[73] On 8 June 2023, Kantate for soli, choir, organ and orchestra was premiered by Andreas Reize conducting Leipzig Gewandhaus Orchestra and Thomanerchor in Leipzig, Thomaskirche, on occasion of the 300th anniversary of Johann Sebastian Bach taking office as Thomaskantor.

[78][79][80] In the 2023–24 season, Widmann was Berlin Philharmonic's Composer in Residence and made his debut conducting the orchestra.

[85][86] According to Bachtrack, Widmann was in 2023 the third most performed living contemporary composer in the world, behind John Williams and Arvo Pärt.

[91] In his experimental and technically demanding early work,[92][93][94] Widmann integrates serialism and noise in traditional sources.

[97][95] In many of his compositions, Widmann is in a musical "dialogue" with Classical and Romantic composers such as Mozart,[98] Beethoven,[99][100] Schumann,[101][102] Mendelssohn,[103][104] Schubert[105][106] and Brahms.

[99][45] Beside the influence of his musical idols, Widmann finds inspiration in literature, poems, paintings and sculptures.

[112] He frequently uses literary sources for his compositions, like Matthias Claudius, Klabund, Heinrich Heine, Peter Sloterdijk, Clemens Brentano and Friedrich Schiller in his oratorio ARCHE.