Literature advocates that at the heart of inclusive education is collaboration and leadership. Despite Greece and England ́s theoretical agreement on inclusion, what is less clear is how this is enacted in practice. This qualitative comparative multi case study investigated the role of school leadership in promoting inclusive education and social justice through the lens of Collaborative Professionalism (CP). The goal of the comparison was to share information about both countries and to positively influence one another. An interpretivist ontological stance was adopted and 47 participants took part in this study. Data collection methods included semi-structured interviews, observations, visual methods and sociograms. NVivo R and thematic analysis were employed for this study. Findings suggested that rejecting authoritarian approaches that leave little or no space for teacher initiative play a crucial role in promoting an inclusive ethos. The Greek centralised system appeared to allow very little space for teacher collaboration in contrast to the English where collaborative practices were encouraged by the school leaders. Including community members and students while building collaboration across schools and systems seemed to lead to more inclusive practices. The decentralised system, contrary to a centralised one, along with a more organic style of leadership offered more opportunities for the creation of inclusive cultures. Future research should focus on decentralised educational systems and how school leaders can empower teachers to develop collaborative practices. Governments and higher education policymakers could explore developing national educational policies that would give priority to collaborative teamwork, PD, establishing common ethos and vision for all staff in both countries.