This thesis investigated the application of transformational leadership (TL) in the higher education (HE) research supervision context, with a specific focus on mechanisms underpinning leader effectiveness. In Chapter 1, the concept of TL is introduced, and the current research in HE briefly reviewed. The chapter highlights the suitability of the context for study in TL, and the need for research with a focus on mechanisms. In Chapter 2 the issue of contextually valid measurement is addressed. In a two-phase study (N = 389), the measurement properties of the Differentiated Transformational Leadership Inventory were explored using conventional confirmatory factor analyses (CFA) and bi-factor models. Traditional CFA confirmed the eight-factor structure of the scale in the supervision context, while bi-factor models revealed a dominant general TL factor. Consequently, an abbreviated global scale was developed using the factor analyses and confirmed using multi-level CFA. In Chapter 3, two studies examined the role of several variables as mediators of the TL-performance relationship. Mediation analysis in Study 1 (N = 155) showed mixed support for the hypothesis that transformational leadership would positively impact grade performance via its influence on leader-member exchange, needs satisfaction and engagement, sequentially. A second study (N = 139) incorporating a time lag between leadership and LMX showed more positive support for the proposed indirect effects. Findings suggest that LMX, need satisfaction and engagement are important mechanisms underlying the effectiveness of TL. Chapter 4 examined the role of students’ implicit theories of ability as an alternative mechanism. A rationale is proposed whereby transformational supervisors may develop incremental beliefs of ability in their students that subsequently enable them to cope more effectively with setbacks. A sample of 421 PhD students completed an online questionnaire measuring TL, their implicit beliefs of ability in their PhD, and their coping styles. Mediation analyses provided some support for the hypotheses, demonstrating an indirect effect of transformational leadership on approach coping via students’ entity beliefs. Finally, in Chapter 5 the theoretical and applied implications of the thesis findings are discussed in relation to existing research. Overall, the findings of the thesis emphasise the applicability of transformational leadership to the HE supervision context, having demonstrated its direct and indirect relationship with key student outcomes including grade performance. Furthermore, the results provide insight into the mechanisms of transformational leader effectiveness that may aid practitioners in their own supervision practices. Finally, the thesis presents two new scales for the measurement of transformational leadership in the HE context for use by practitioners and researchers alike.