Flemming's musical career started with "pigtråds"-music and "syrerock" in Odense with groups such as After Shave, Ahasverus and Rådkøl & Flæskesteg, and on to Funen folk music with Fynboerne and Evald Thomsen. Then there was folk rock with Folkstow in Aarhus, country music with Countryekspressen, recording with Peter Belli and performances at the Midtfyn, Tønder and Roskilde Festivals with the Danish punk-folk band Familieorkestret. He was with Hokus Poulsen a permanet orchestra at Hansens Værtshus and at Avisen Fyn's many parties in one of Odense's most fertile musical periods. Hokus Poulsen was part of Rock-Nalle's (see Nalle) revival in the early 1980s, where they backed Nalle for a year. Since 2010 he has cultivated roots and country in Midnight Special, Back on the Horse, Morsing Schroeder project and Midnight Special Revisited.

Alongside his career as a musician, Flemming has played a role in the organization of Danish Rock Music, and he has been involved in building De Rytmiske Aftenskoler, De Danske Musikkontorer (see Århus Musikkontor and Københavns Musikkontor), "ROSA - The Danish Rock Council" (see Hansens Værtshus) and most recently Denmark's Rock Museum Ragnarock. He was a member of Statens Musikråd in 1983-1991 and was director of the Danish Music Information Center from 1992-1996. Today (2022) he is a member of the Danish Rock Academy.