According to the Market Studies literature, markets are not stable structures but evolving plastic entities, open to market shaping attempts by the actors who generate their form. Market shaping occurs through interdependent processes involving institutionalized practices and intentional activities of market actors. Existing literature has so far focused on firms with a narrow scope, i.e. firms that represent either side of the traditional seller/buyer division, hold well-established positions in traditional product or service market, and strive almost exclusively for financial growth. Using a case study, I integrate the institutional work framework as a lens to examine how a sustainable new venture (SNV) in an intermediary role attempts to shape the market for Guarantees of Origin (GO) for renewable electricity. The study provides a fresh way to examine change agency in market transitions towards sustainability. Different types of market shaping actions are identified and connected to the main elements of the GO market. The initial findings of this work-in-progress paper describe how the focal firm attempts to drive market development while facing institutional persistence.