Early life 
His mother, the singer Iraida Jansons, who was Jewish, gave birth to him 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, the young Mariss first studied violin with his father.
In 1946, his father 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 Jansons 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 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.
In 1997, Jansons became the music director of the Pittsburgh Symphony Orchestra. His initial contract was for three years, but his subsequent contract renewals were evergreen contracts that required yearly renewal. In June 2002, he announced his departure from the orchestra in 2004.
In April 1996 in Oslo, Jansons nearly died while conducting the final pages of La bohème, after a heart attack. He recuperated in Switzerland. Later, surgeons in Pittsburgh fitted a defibrillator in his chest to give his heart an electric jolt if it fails. (Jansons's father died at a 1984 concert, conducting the Hallé Orchestra). Jansons has stated that he suffers from jet lag, and this was one reason that he left his American position.
At the start of the 2003/2004 season, Jansons began his tenure as chief conductor of the Bavarian Radio Symphony Orchestra (BRSO), for an initial contract of 3 years His commitment with the BRSO is for 10 weeks per season. In September 2006, Jansons extended his initial BRSO contract to August 2009. In July 2007, he further extended his contract with the BRSO to August 2012. In April 2011, he extended his BRSO contract to August 2015 in Munich. He has regularly campaigned for the construction of a new concert hall for the orchestra.
In October 2002, Jansons was named the sixth chief conductor of the Royal Concertgebouw Orchestra (KCO, Dutch abbreviation) of Amsterdam, effective 1 September 2004, succeeding Riccardo Chailly. His initial Amsterdam contract was for 3 years, and his commitment in Amsterdam is for 12 weeks per season. As of October 2012, whilst no published reports of the continued length of Jansons' tenure with the KCO have been given, Jansons continues to serve as the orchestra's Chief Conductor.
In 2006, Jansons conducted the Vienna Philharmonic New Year's Concert for the first time. Also in January 2006, he was awarded MIDEM's Artist of the Year Award in Cannes. In October 2007, Jansons (who himself is Lutheran) conducted Beethoven's Ninth Symphony with the Bavarian Radio Symphony Orchestra for Pope Benedict XVI and 7000 other listeners in the papal audience hall (Auditorio Paul VI). Jansons conducted the Vienna New Year's Concert for the second time in 2012. The concert was televised worldwide in seventy-three countries.
Personal life 
Jansons has been married twice. He and his first wife, Ira, had a daughter, Ilona, a pianist who currently works at the Mariinsky Theatre. The marriage ended during his tenure in Oslo. Jansons and his second wife Irina, a former speech therapist, have a home in Saint Petersburg, where Jansons keeps his collection of scores.
Jansons has been awarded various Austrian and international honours for his achievements, including Commander of the Royal Norwegian Order of Merit from King Harald of Norway and memberships of the Royal Academy of Music in London and the Society of Music Friends in Vienna (Gesellschaft der Musikfreunde). In May 2006, he was awarded the Order of the Three Stars (2nd class or Grand Commander), Latvia’s highest state honour. He was awarded the Bavarian Order of Merit in 2007 and in 2010, the Bavarian Maximilian Order for Science and Art. In 2008, Jansons received the Austrian Cross of Honour for Science and Art.
Jansons' recording of Shostakovich's Symphony No. 13 with Sergey Aleksashkin (bass) and the Bavarian Radio Symphony Orchestra and Chorus won the Grammy Award for Best Orchestral Performance at the 48th Grammy Awards.
On 31 March 2013 Jansons was awarded a medal of honour "For the Merits before St.Petersburg".
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- Mariss Jansons at Allmusic