In 1899 the Nationaltheatret, which were to present both theatre and opera, was opened. Here the orchestra expanded to 44 musicians, and it was conducted by Johan Halvorsen. The orchestra served the Nationaltheatret in two roles: providing music for the new theatre, and symphony concerts for the Music Society. During the First World War, the desire for symphonic music grew, along with inflation, leading to a dispute between the orchestra and the Nationaltheatret and a temporary collapse of the Musikerforening's concerts. Thus, in 1919, the orchestra was reformed as the Filharmonisk Selskaps Orkester (Orchestra of the Philharmonic Company) by private shareholders and initiative. The first season was shared by three conductors; Johan Halvorsen, Georg Schnéevoigt and Ignaz Neumark.
Filharmonisk Selskaps Orkester's first concert took place in Logen (Store Sal) the 27. of September 1919, with 59 musicians on stage and with Georg Schnéevoigt as conductor. On the repertoire was Rikard Nordraak’s Ja, vi elsker, Johan Svendsen’s Fest polonaise, Christian Sinding’s Symphony no. 1, Edvard Grieg’s piano concerto in a minor, and finally Landkjenning, with the singer Erik Bye as baryton soloist. Among the guest musicians this first season were the pianists Eugen d'Albert, Edwin Fischer, Wilhelm Kempff, Ignaz Friedmann and Arthur Schnabel, and the violinists Bronislaw Huberman and Carl Flesch, in addition to the internationally famous conductor Arthur Nikisch. Between September 1919 and May 1920, the orchestra gave 135 public concerts, and most of these were sold out.
The next decades bore strong evidence of economical problems, which even led to the resignation of 15 musicians in one season. Still, artistically, the progress was enormous, and the orchestra attracted several famous musicians and conductors, such as Richard Burgin, who later became concertmaster for Serge Koussevitzky in Boston; Max Rostal, Ernst Glaser and Robert Söetens, for whom Sergei Prokofiev's 2nd Violin Concerto were written; and Stravinsky and others who were driven out of Germany by the Nazi regime - Fritz Busch, Erich Kleiber, and Bruno Walter. The first Norwegian radio broadcast took place in April 1923, and shortly after, the first radio concert with the Oslo Philharmonic Orchestra. From 1925, there was a contract between the orchestra and the Norwegian Broadcasting Corporation (NRK), ensuring weekly live broadcasted concerts. This contract with NRK, came to be what saved the orchestra from bankruptcy in the 1930s.
In 1931, Dobrowen left Oslo, and the position as chief conductor was divided between two Norwegians: Odd Grüner Hegge and Olav Kielland, and from 1933, by Kielland alone. Kielland kept the position until 1945. During Second World War, the musical life in Norway was going through a difficult period, with musicians coming from both sides, and with censorship, boycotts and fist fights in the concert halls. Still, Ernst Glaser kept the position as concert master until 1969, only interrupted by three years in exile.
In 1979 the name was changed to Oslo Philharmonic Orchestra, and in 1996 the organization was made an independent foundation by an act of the Norwegian parliament.
In 1953 Oslo hosted the ISCM Festival, which brought further international contacts in the awareness of new repertoire, which many of the Scandinavian countries had been deprived of during the years of World War I and World War II. The first performance of the Oslo Philharmonic outside Scandinavia took place in 1962, where it made a striking appearance on the international stage. Since then, the orchestra has much international acclaim.
Although the orchestra has maintained high standards of quality since its inception and under various renowned musical directors, many consider that it saw its largest leap forward during the tenure of Mariss Jansons from 1979 to 2002. During this time the orchestra recorded authoritative renditions of Tchaikovsky's symphonies, and international tours. The Oslo Philharmonic won international acclaim with its Tchaikovsky cycle and a very successful series of recordings for EMI. In 2000 the orchestra completed a cycle of Bartók for Simax, and plans to follow this with a cycle of works by Mahler.
The Oslo Philharmonic holds an average of sixty to seventy symphonic concerts annually, the majority of which are broadcast nationally on the radio. The orchestra also performs chamber concerts frequently throughout the year. In the past decade, the Oslo Philharmonic has performed in a number of international venues, including but not limited to Austria, Belgium, Denmark, France, Germany, Holland, Italy, Spain, Sweden, Switzerland, the UK, Canada, China, Hong Kong, Japan, Korea, Taiwan and the United States. Future tours are planned under the new director Saraste to locales such as the US, Great Britain, Austria, Germany, Spain and Romania.