Nils Henrik Asheim, born in Oslo in 1960, made his debut as a composer at the age of 15, when his wind quintet Octopus was performed at the Nordic Youth Music Festival in Helsinki in 1975. At that point he had already been studying composition under Olav Anton Thommessen for three years.

When he was 18 years old, he was awarded second prize in the under-35 category at the European Broadcasting Union's Rostrum in Paris for the work Ensemble Music for Five. The following year he began his studies at the Norwegian State Academy of Music, where he took degrees in church music (1981) and composition (1987). Asheim also performs as an organist and pianist after having studied under Professor Harald Herresthal and Geir Henning Braaten, respectively.

From 1982 to 1984 Asheim was composer-in-residence at the Rogaland Conservatory of Music. He was then awarded a Dutch government scholarship to spend a year at the Sweelinck Conservatory in Amsterdam, where he studied composition under Ton de Leeuw and Electro-acoustic composition at the conservatory studio.

Asheim has received the Norwegian Society of Composers' "Work of the Year" award on two occasions: in 1982 for Window, and in 1986 for Water Mirror. 2002 saw the composer awarded the Edvard-prize for “Chase”. In 2007 he was awarded the Arne Nordheim Composers' Prize. Central works include “ Mirror ” for orchestra as well as “Turba” for orchestra, choir, soloists and electronic parts (the work was nominated to the Nordic Council’s Music Prize).

Asheim’s works have been featured at several official ceremonies such as the 1994 Lillehammer winter Olympics and the 2001 Royal Wedding. His production consists mainly of chamber music, church music and orchestral works as well as pieces for music-theatre. Electro-acoustic means are present in several of Asheim’s compositions. Asheim’s fascination for sonorous exploration in various architectonic settings is evident in such works as the church opera The Ascension of Martin Luther King and outdoor-performed works Blowout and Strandhogg.

Asheim's musical idiom reflects a modernistic attitude, at the same time concerned with clarity and often a "physical" directness. His early works are based on development of short, simple motifs. Asheim has subsequently developed an interest in the complex juxtaposition of musical elements, such as for example in his trilogy Water Rings, Water Mirror and Mirrors.

One can sense a shift in compositional methods in Asheim’s newer works – his post-2000 compositions mark a depart from the idea of linear development. Asheim’s work now feature compositions that are constructed as various “rooms” which he enters and exits throughout the piece. The compositional material is present already at the piece’s beginning and the subsequent musical course is devoted to viewing it from different angles. Listening to his works takes the form of exploration of possibilities rather than a continuous process through new stages. Asheim’s aim is to combine rigid, architectonic structures with the spontaneous vigour found in improvised music. Such an approach is well illustrated on the CD "Broken Line" (featuring Vertavo String Quartet) withe the work of the same title as well as Navigo, Chase and Nicht, all from the early 2000's. Asheim’s improvisational experience inspires his compositional approach – performers are often challenged to stretch the written material’s limitations, thus bringing the performance into a musical “no-man’s-land”. Another indication of the improvisational influence found in Asheim’s works is the composer’s use of parallel, non-synchronised layers that are joined at calculated but not controlled intervals.

Asheim has shown a strong interest for music theater, obvious in his monodrama "Degrees of White" for speaking voice and orchestra. Working on classical repertoire is another field of interest of his, manifested in the CD project "Mazurka - remaking Chopin" with Gjertrud's Gypsy Orchestra. For this recording, Asheim was awarded his second Spellemanspris (Norwegian Grammy).

Asheim is also an active organ improvisator. A long-standing and fruitful collaboration with vocalist Anne-Lise Berntsen has resulted in two CDs: Engleskyts and Kom Regn – both are recorded in Southern Germany using rare baroque instruments. 16 Pieces for Organ is a solo-improv album featuring the Oslo Cathedral organ, an instrument for which Asheim has written the 1998 inaugural work Salmenes Bok for choir and two organs. "19 March 2004, Oslo Cathedral" is a live concert recorded on CD that was awarded the Spellemannsprisen (Norwegian Grammy).

As an organ player, Nils Henrik Asheim has ongoing duo collaborations with musicians from jazz and electronic music fields, like Paal Nilssen-Love and Lasse Marhaug.

Nils Henrik Asheim was president of the Norwegian Society of Composers from 1989 to 1991. Since 1991 he has lived in Stavanger, where he has been strongly involved as well in the classical music organizations as in the contemporary arts scene: as leader of Ny Musikk (Contemporary concerts organizer), co-founder of improv collective Kitchen Orchestra, and not the least the driving force behind the contemporary arts center Tou Scene, since its founding in 2001.

From September 2012, Asheim is appointed organist at Stavangers Concert Hall (Stavanger Konserthus). As such, he has artistic responsibility for the new 65-voice instrument from Ryde & Berg.