He studied with Knut Bjærke and Torleif Nedberg at the Norwegian Academy of Music and with Roger Birnstingl at the Geneva Conservatory. He continued his studies with Gwydion Brooke in London and subsequently Valeri Popov in Moscow.
From 1981 to 2007 he was the principal bassoonist of the Stavanger Symphony Orchestra, a position he also held for a period in 1988 with the Stockholm Philharmonic Orchestra.
Rønnes was the first Norwegian bassoonist to receive support from NorConcert—the Concert Institute of Norway—for his début concert at the University Aula in Oslo in 1985. In addition, he has established himself as a highly regarded chamber musician and as an ardent advocate of Norwegian contemporary music; several Norwegian composers have dedicated works to him, resulting in several recordings.
He is in much demand as a soloist in Europe, Russia, China, and the USA and has given bassoon master classes in several music universities in Scandinavia, France, China, and Russia's Tchaikovsky Conservatory in Moscow.
He is also the teacher of Prof. Dag Jensen, Prof. Ole Kristian Dahl, and his son Kristian Oma Rønnes.
In addition to his career as a performer, Rønnes also works as a composer and was a member of the Society of Norwegian Composers from 1992 to 2018, when he resigned his membership. His works have been performed in many countries around the world and are constantly attracting a wider audience. He has received several commissions funded through the Norwegian Cultural Council. Rønnes has restored about 30 works from various composers, with his major projects being the restoration of works by Harald Saeverud in addition to the works of Arvid Kleven, resulting in several recordings by the Stavanger Symphony Orchestra on the BIS Records label. In May 2007 he was awarded the Government Grants and Guarantee Income for Artists (Norway) to support his research in restoring and performing Norwegian bassoon music.