Various cultural intermediaries have become involved in connecting graffiti writing to the art market. Through this case study, I shed light on the division of intermediation labour in the commercialization process of artworks stemming from subcultures in a global art market. Since the early 1970s, an international network of cultural brokers has gradually been set up in a frontier zone between art collectors and graffiti writers. Interviews, documentary sources and participative observation as an insider made it possible to identify these intermediaries and their specific roles and resources. My investigation sheds light on three historical phases of intermediation: from the first initiatives in New York in the 1970s to thematic auctions in French between 2006 and 2017. The first two phases ended in commercial and critical failure, first in American galleries and then in European museums, but the third phase led to economic success on the secondary art market, followed by public institutions’ validation. Three types of intermediaries are distinguished: commissioned experts from graffiti subculture, who select and encourage graffiti writers to produce marketable works; entrepreneurs, who seek to create a niche in the art market and promote a flattering image of graffiti art collectors, a group to which they often also belong; established auctioneers, who mobilize influential art buyers and encourage their favourable reception of graffiti artworks in order to expand their business. Whether they collaborate or compete with each other, these cultural intermediaries have complementary roles and resources linked to their social trajectories. However, they reap unequal benefits from their activities, whose impact on subcultural practices is finally discussed.