His career included a position as principal oboist in the Danish National Symphony Orchestra, (1979 to 1990) performances in Europe, USA and Japan as soloist and chamber musician.
Niels Eje has composed and arranged a large repertoire for different classical ensembles as well as music for concerts, theatre, TV and documentaries.
He is the founder of Trio Rococo (harp, Berit Spaelling, oboe Niels Eje, and cello, Inge Mulvad,) whose album 'Norwegian Wood' was released worldwide.
Niels Eje has participated on several recordings with various artists in a number of genres, including with Miles Davis on the album Aura, and with Niels-Henning Ørsted Pedersen, Berit Spaelling, Inge Mulvad in the album In the Name of Music In 1998 Niels Eje founded the interdisciplinary project Musica Humana Research together with Professor Lars Heslet, Copenhagen University Hospital.
The research projects were aimed at creating a new specially designed music environment in hospitals and with scientific methods documenting the effect.