In recent years, Mayrhofer has made debut appearances with the Norwegian Radio Orchestra, the Britten Sinfonia at the Aldeburgh Festival, musicAeterna at Zaryadye Hall in Moscow, and at the Salzburg Festival, as well as performing at the Klangspuren Festival with both the Tiroler Sinfonieorchester and the Orchestre National Bordeaux Aquitaine.

He has conducted renowned ensembles such as Staatskapelle Berlin (premiere of his oratorio «Wir sind Erde» at the Berlin Philharmonic), Bavarian State Orchestra, Bamberg Symphony, Württemberg Philharmonic Reutlingen, Slovenian Philharmonic, and Belgrade Philharmonic, and continues to receive regular invitations from Munich Symphony, Bamberger Symphoniker and Het Collectief (Belgium). Gregor also conducted the recording of the movie soundtrack of «Das Kanu des Manitu» (Manitu’s Canoe) by Ralf Wengenmayr with the German Film Orchestra Babelsberg.

His conducting credits include many contemporary music ensembles such as Hong Kong New Music Ensemble, Austrian Ensemble for New Music (ÖENM), Ensemble Intercontemporain, NAMES Ensemble Salzburg, Ensemble Ascolta (Stuttgart) Ensemble Kontraste (Nuremberg) and the Scharoun Ensemble of the Berlin Philharmonic. He has also worked with renowned soloists such as Daniil Trifonov, Khatia Buniatishvili, Patricia Kopatchinskaja, Georg Nigl, Martin Helmchen, Christoph and Julian Prégardien.

Mayrhofer served as assistant conductor to Kirill Petrenko and Sir Simon Rattle at the Berlin Philharmonic, and has continued to assist Sir Simon with the London Symphony Orchestra, notably on the production of Tristan in Aix-en-Provence. Further assistantships have taken him to the Staatsoper Unter den Linden, the Vienna State Opera, and from 2015 to 2017 to the Ensemble Intercontemporain, where he made his conducting debut at the Paris Philharmonic in 2016, filling in for Pablo Heras-Casado at short notice.

As a composer, Mayrhofer’s music has been performed by the Bavarian State Opera, the Bavarian Radio, the Frankfurt Radio Symphony Orchestra, the Cologne Philharmonic, the Residentie Orkest Den Haague, the Norwegian Radio Orchestra, the Arctic Philharmonic, the Asasello Quartet, and the Schwetzingen Festival. He has received further commissions from the Munich Biennale, the Deutsche Oper Berlin, the Hanover State Opera, and the Tyrolean Festival Erl, among others. In 2023, Mayrhofer was nominated in six different categories of the Opus Klassik awards for both his conducting and composition. His work Recycling Concerto, in particular, was highlighted among these nominations.

Mayrhofer studied conducting at the prestigious Juilliard School in New York with Alan Gilbert, and pursued composition studies at the Munich University of Music and Performing Arts (with Jan Müller-Wieland), the Paris Conservatoire (with Frédéric Durieux), and the Robert Schumann Academy in Düsseldorf (composition with Manfred Trojahn and conducting with Rüdiger Bohn).

As a pianist, he performs with his brother Raphael in the jazz duo Imbrothersation.