One of the two main tasks of innovation leadership, a practice to inspire and enable creativity and innovation in organisations, is to construct a creativityenabling organisational environment. One form of this main task is using developmental interactions, like mentoring, as innovation leadership practices. A hackathon is one type of innovation contest with three designed phases: pre-hackathon, hackathon event and post-hackathon, involving multiple stakeholders with distinct roles, such as hackers and mentors. In a hackathon, the central activity of mentors is to support the hackers’ innovation process, especially in idea creation and concept development. The mentor role has not been focal in hackathon studies; thus, this chapter addresses the role, impact, and ways to acknowledge the mentors as an integral, contributing innovation leadership practice in hackathons. As an empirical study, this chapter presents the results of a public sector case in a Swedish multi-disciplinary municipality conducting intra-organisational hackathons in three different collocations. The chapter contributes to the literature on innovation leadership at the team level with mentorship in innovation contests in the public sector context by revealing the dual-role tension of innovation leadership in mentor activities in the hackathon event phase from both the hackers’ and mentors’ viewpoints, and the necessity of mentor-benefitting training in pre-hackathon phase.