In the 2018 Järvi Conducting Academy in Estonia, he was taught by Paavo Jīarvi as well as his father, Neeme Järvi, and in 2019 he received a Conducting Seminar Fellowship from the Tanglewood Music Center with the Boston Symphony Orchestra, Adris Nelsosn, and Stefan Asbury. After winning an Aspen Conducting Prize as the Aspen Music Festival in the summer of 2021 as a Conducting Fellow of the American Conducting Academy, he received a reinvitation to 2022.

He was the first composer-in-residence at the Brucknerhaus Linz for the season 2020/21. In 2019 he won the 1st Prize of the Organ Composition Competition by the Bruckner Private University and Brucknerhaus Linz, and obtained a commission from the International Mozarteum Foundation for his opera Lob des Schattens, was staged in Salzburg. His accolades include the 1st Prize at the Franco Donatoni Composition Competition in Milan (2019) and Herbert von Karajan Award for his work as a composer and conductor (2023). In 2021 he was accepted as conducting fellow into the Forum Dirigieren of the Deutsche Musikrat.

He currently serves as Assistant Conductor with the Berliner Philharmoniker. He secured a two-year position as a conducting fellow at the Karajan Academy, being awarded the Siemens Conductors Scholarship after winning the conducting competition at the Philharmonie Berlin in 2021. In addition to assisting Chief Conductor Kirill Petrenko in both concert and opera performances, Oscar conducts independent concert projects in collaboration with the academy members of the Berliner Philharmoniker. 2021 also saw Oscar appointed Assistant Conductor at the Philharmonie de Paris with the Ensemble intercontemporain and Music Director Matthias Pintscher.

In recent seasons, he made guest appearances at the Salzburg Easter Festival (2023), International Shostakovich Festival in Gohrisch, International Bruckner Festival in Linz (2022), the Berlin Symphony Orchestra, Beethoven Orchestra Bonn, Munich Radio Orchestra, and Ensemble Intercontemporain in Paris. As a conductor or conducting assistant under Sir Simon Rattle, Esa-Pekka Salonen, Reinhard Goebel or Hartmut Haenchen, Oscar has worked with the Bavarian Radio Symphony, Sächsische Staatskapelle Dresden, Philharmonia Orchestra, Klangforum Wien, Verbier Festival Chamber Orchestra, Deutsche Kammerphilharmonie Bremen, and the Cyprus Symphony Orchestra. In the2024/25 season, he follows invitations from the Semperoper Dresden with the Sächsische Staatskapelle, Munich Philharmonic, Deutsches Symphonie-Orchester Berlin, Bamberg Symphony Orchestra, Vienna Konzerthaus with the ORF, the Philharmonic orchestras of Copenhagen, Bremen, the SWR Symphony, Neues Bachisches Collegium Musicum, Gewandhaus Orchestra, Stuttgart Chamber Orchestra, and Ljulbjana Radio Orchestra. He also tours with the Camerata Salzburg and pianist Mao Fujita in Salzburg, Munich and Vienna and returns to the Gewandhaus with the Mendelssohn Orchestra Academy, Gürzenich Orchestra Cologne, and Tonkünstler Orchestra Vienna.

In the past years he was a lecturer at Salzburg College teaching composition and was invited as visiting lecturer for algorithmic composition at the Indian Institute of Technology in Hyderabad in 2019.