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.
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.