Gunnar began his career in the music industry in the mid 1990s, when he established the Norwegian hip-hop group Spetakkel. The group went on to release two full-length studio albums and two EP's, before reaching their end. He then went on to pursue his solo career under the moniker Gest.
Since then, Gunnar has filled numerous roles in the Norwegian music industry, primarily representing a number of Norwegian and Swedish artists within the urban and pop segment. He has also served as a judge on the Norwegian Idol for 5 seasons.
Greve is the founder and current managing partner of Norwegian full-service company MER, representing artists such as Alan Walker. Gunnar has played an important part in the development of Alan Walker as an artist, both in the role of manager, A&R and songwriter. Earlier this year, he was appointed Managing Director of Liquid State, the new joint venture formed by Tencent Music and Sony Music, and now he splits his time between Oslo and Shanghai.