This paper describes research that aims to develop an argument visualization tool and associated method for supporting eParticipation and online deliberation. Based on the state-of-the-art in the field of computer-supported argument visualization, the tool will support the work of relevant eParticipation actors by enabling them to navigate through arguments contained in relevant consultation and policy documents. This tool will form the core of our investigation into the mediating role that large, Web-based argument maps can play in eParticipation scenarios. In particular, we intend to investigate the method and practice of how various eParticipation actors use the tool in the policy-making process. To this end, this paper sets out a clear research agenda for research at the intersection of eParticipation and computer-supported argument visualization.