Mariss Ivars Georgs Jansons (born 14 January 1943) is a Latvian conductor, the son of conductor Arvīds Jansons and the singer Iraida Jansone.
Iraida Jansone, who was Jewish, gave birth to her son in hiding in Riga, Latvia, after being smuggled out of the Riga Ghetto, where Iraida's father and brother were murdered by the Nazis. As a child, Jansons first studied violin with his father.
In 1946, Mariss's father, Arvīds Jansons won second prize in a national competition and was chosen by Yevgeny Mravinsky to be his assistant at the Leningrad Philharmonic. When his family joined him in 1956, young Mariss entered the Leningrad Conservatory, where he studied piano and conducting, although his father urged him to continue playing violin. In 1969, he continued his training in Vienna with Hans Swarowsky and in Salzburg with Herbert von Karajan. Karajan had invited Jansons to be his assistant with the Berlin Philharmonic, but the Soviet authorities blocked Jansons from ever hearing about the offer.
In 1973, Jansons was appointed Associate Conductor of the Leningrad Philharmonic Orchestra (now the Saint Petersburg Philharmonic Orchestra). In 1979, he was appointed music director of the Oslo Philharmonic, with which he performed, recorded and toured extensively. Jansons resigned his Oslo position in 2000 after disputes with the city over the acoustics of the Oslo Concert Hall.
In 1992, Jansons was named principal guest conductor of the London Philharmonic Orchestra. He has worked as a guest conductor with the London Symphony Orchestra and has recorded Mahler's Symphony No. 6 with them for the LSO Live label.