The needs of Quebec students, which have become increasingly diverse and evolving in recent years (Government of Quebec, 2020), call for a change in teaching practices. To achieve this, the development of a mechanism following the principles of the learning organization, such as a professional learning community (PLC), within the school can support these changes. Although principal leadership is likely to be a lever, its influence has been little documented in a Quebec elementary school context. This study therefore examined the influence of principal leadership on the activity of a learning organization, using Engeström's (2000, 2001, 2011, 2015) activity theory. This descriptive qualitative study mobilized the case study approach, involving in an elementary school in the Eastern Townships in which the classroom teachers work in PLC. Semi-directed individual interviews were conducted with the school principal and five teachers. Our analyses show that the principal's leadership contributes to resolving many of the contradictions that can arise in a system of activity, and thus promotes its transformation.