Research on how start-up firms utilize networks has focused on direct effects of either the personal network around the entrepreneur or the formal collaboration network around the firm. Combining those approaches, we model how a firm’s collaboration network is embedded in the personal network around the entrepreneur. With data from the Global Entrepreneurship Monitor on 8918 start-up firms in 40 countries surveyed during 2012–2013, we examine (1) how entrepreneurs’ networking in private and public spheres is impacting firms’ collaborative networking, (2) how both the personal network and the firm network are impacting performance in forms of innovation and exporting, and (3) how embeddedness of the firm network in the private and public sphere networks around the entrepreneur is affecting innovation and export. The analyses show that the firm network as well as innovation and export are enhanced by the networking in the public sphere, but reduced by networking in the private sphere. Moreover, the benefits of firm network for innovation and export are strengthened by networking in the public sphere but weakened by networking in the private sphere. Finally, we find that innovation is a driver for export, and that this benefit is enhanced by networking in the public sphere, but decreases with networking in the private sphere. These findings refine our knowledge of the functioning of firms’ networking for innovation, especially the positive effects of networking in the public sphere and negative effects of networking in the private sphere.