Leadership has been of the highest interest for decades as leaders are one of the main factors for organisational success. However, when understanding start-ups the classical leadership theories lack insight into how a leader can grow and thrive together with the organisation. The most used theories today determine what is generally understood as good and bad leadership styles. However, these fail to incorporate the start-ups' unique position and the leaders´ dynamic relationship with their organisation. Start-ups act in new, uncertain environments and more than two-thirds end up failing before growing into an established organisation. The critical phase in which the leaders could affect whether a start-up shall grow or fail is called the transition phase.  This study therefore aims to understand the perspective of leaders in start-ups through growth. By looking through the leaders' perspective, the study investigates how the transformational- and transactional leadership affect start-ups through growth. The second aim of the thesis is to gain a further understanding of the managerial challenges leaders face due to start-up growth.  The study was conducted through qualitative interviews with CEOs and top managerial founders of start-ups in the Northern region of Sweden. The studies managers had all been part of the organisation's growth journey and provided unique insights into the mind of a leader.  The findings portray two main trends of leadership, proactive and reactive. These findings provide insight into the importance of knowledge and positive attitudes toward change as contributing factors for proactively working towards adaptation and development. The findings also portrayed that managerial challenges are mostly connected to the lack of knowledge of leadership. The study concludes with a proposed framework, introducing a complementary dimension to the body of literature on leadership and growth. The dimensions are “Knowledge of leadership” and “Positive attitudes of change”.