Jan Koetsier was born on 14 August 1911 in Amsterdam, the son of the singer Jeanne Koetsier and the teacher Jan Koetsier-Muller. From an early age he received musical encouragement and support (piano lessons). Koetsier decided to study music early on, entering college straight after leaving school. He moved to Berlin in 1913 with his family, and aged 16, was the youngest student of his day to pass the entrance audition in piano to the Berlin Hochschule für Musik. There, as well as studying piano, he studied score-reading and music theory with Walther Gmeindl, and conducting with Julius Prüwer from 1932. Also encouraged by Artur Schnabel, signs of his future direction in music began to emerge – composing and conducting. In 1933, Koetsier took up a position as a répétiteur at the Stadttheater in Lübeck. But after just one concert season, he returned to Berlin and began working as a conductor touring with theatre ensembles such as the ‘Deutsche Musikbühne’ and the ‘Deutsche Landesbühne’; his repertoire expanded to include music theatre works.

From 1936/37 he had the opportunity of working as a freelance conductor for the short-wave broadcasting station in Berlin, directing broadcasts of his own folk music arrangements, including arrangements of South American and African songs. Because of the political situation, Koetsier gave up his position at the Berlin radio station in 1940 and took up an offer of working as piano accompanist to the dancer Ilse Meudtner on a year-long tour. Following on from this, he worked as conductor of the newly-founded Kammeropera in The Hague, during which he travelled to numerous Dutch towns and cities (1941/42). He then became second conductor of the ‘Concertgebouw Orchestra’ in Amsterdam (1942-48), a central point in his artistic development, which brought with it valuable stimuli and experience, including collaborating with the orchestra’s chief conductor, Willem Mengelberg.

He then spent a short period as conductor of the ‘Residentie Orkest’ and as conducting teacher at the Royal Conservatory in The Hague before being invited by Bavarian Radio to become principal conductor of its newly-founded Symphony Orchestra in 1950. Koetsier held this position for sixteen years, working intensively on studio productions of all periods and styles which were required for daily broadcasting. He also conducted public concerts, including some in the Bavarian Radio ‘musica viva’ series. In 1966 he became professor of conducting at the Hochschule für Musik in Munich, in which position he was involved in reforming the teaching schedule.

After his retirement, Koetsier concentrated mainly on composing at his home in Rattenkirchen, Upper Bavaria. In these years, he founded the International Jan Koetsier Competition for the encouragement of young brass ensembles, since 1999 at the Hochschule für Musik und Theater Munich.
Koetsier’s work with instrumental soloists and ensembles led to numerous commissions. Musicians he frequently worked with included the ‘Philip Jones Brass Ensemble’, the ‘Trio Armin Rosin’ and the ‘Brass Philharmonie’ founded by Armin Rosin, the ‘Slokar Quartet’, the ‘Rennquintett’, the ‘Leipziger Hornquartett’ and the ‘Münchner Blechbläsersolisten’, as well as numerous string soloists and pianists. For many of these groups, his works have become an established part of their repertoire. The fact that in his composing, Koetsier always bore practical musical considerations and requirements in mind is also a basic reason for his choice of instrumental combinations and scorings; examples of this are his combination of horn and harp (Sonata, Op. 94), four tubas or trombones (‘Wolkenschatten’, Op. 136, for tuba quartet; ‘Die Bremer Stadtmusikanten’, Op. 138, for trombone quartet) or brass quintet and harp (‘Introduction and Variations on the ‘Vyšehrad’ Theme by Friedrich Smetana’, Op. 71). As well as chamber music for wind and strings in various combinations, Koetsier also composed solo concerti (e.g. the ‘Echo Concerto‘ for 2 piccolo trumpets and string orchestra, Op. 124, or the Concerto for Brass Quintet and Orchestra, Op. 133) and numerous orchestral works including symphonies and serenades. Then there is piano and organ music, a few songs, choral works and an opera (‘Frans Hals’, Op. 39).