In 2007, he was appointed as Principal Conductor of the Slovak Radio Symphony Orchestra. Besides conducting numerous studio recordings of works by Slovak modernist composers, he also introduced many previously unperformed classical works into SRSO’s repertory (Franck, Nielsen, Roussel, Glazunov, Ives, Glass and Ginastera). In 2010 and 2014, he successfully toured Japan with his orchestra. In recent years he performed as a guest with Polish National Radio Symphony in Warsaw, with Gdańsk, Zielona Gora, and Szczecin Philharmonic in Poland, Sofia Philharmonic in Bulgaria, Athens State Orchestra in Greece, Las Colinas Symphony in the USA, Jenaer Philharmonie in Germany, Orchestra Sinfonica di Roma in Italy, Cracow Philharmonic in Poland, with Jerusalem Philharmonic in Israel, Krasnoyarsk Philharmonic in Russia, Orquesta de Ciudad Granada, Orquesta Municipal de Murcia in Spain and Daejon Symphony in South Korea.
In 2015, Mario Košik performed as a guest conductor with Orquesta Sinfonica Murcia, with NHK Chamber Orchestra, repeatedly with Szczecin Philharmonic, as well as with Seongnam Philharmonic and Kangnam Symphony in South Korea.