This study examines the development of the Leader–Member Exchange (LMX) relationships of a newly appointed leader. The aim of the study is twofold; first to shed light on the development process of LMX relationships when a new leader enters an organization; and second, to examine the effect of a managerial development intervention that was implemented. The study was executed as a longitudinal single-case study in which a leader and their subordinates were observed and interviewed over a period of approximately one year. The study’s contribution is first to reveal how several critical incidents occurring during the first year of the tenure of a new leader affected the relationships the leader formed. The second contribution is to show how the development intervention supported the leader and the development of the LMX relationships.