Thelin, who was self-taught as a musician, started playing with the dixieland group Pygmé Jazz Band, and later joined the sextet of Putte Wickman.[2] Influenced by Miles Davis among others, he then moved towards modern jazz.[3] Thelin led his own quintet from 1961 until 1965, touring in Europe on several occasions.[1]
Disillusioned with the Swedish jazz scene,[3] Thelin moved to Austria in 1968, where he taught at the Academy of Music in Graz,[1] while also performing free improvised music with a group led by himself and Joachim Kühn in several European countries.[2] After returning to Stockholm in 1972, he led his own Eje Thelin Group in Sweden for the rest of the 1970's,[1] moving towards jazz fusion and experimenting with electronics.[2] Thelin would later mainly devote himself to composing and performing as a soloist.[3]
During his career, Thelin performed and collaborated with Roy Brooks, Graham Collier, Palle Danielsson, Joe Harris, Joachim Kühn, Evan Parker, George Russell, John Surman and Kenny Wheeler.[2]