The thesis reviews recent and current literature on leadership, and in particular on distributed leadership and complexity leadership theories. It describes my research into the factors affecting the success of transition towards a more distributed approach to leadership in two cases: one is a large UK private company and the other is a large UK university. The longitudinal research was conducted over the period from 2011 to 2013, using repeated interviews at senior and middle management levels, document analysis and observation to collect a rich set of data about both cases. I used a template to help analyse the data from each case. Through subsequent cross-case analysis the thesis identifies certain factors that influence the degree of success in making the transition to a distributed form of leadership, which involves not only devolved decision making but also increased levels of collaboration and organisational agility, which are key concerns of leaders of large organisations according to recent research across top 250 companies in the UK (Ipsos MORI, 2015: 5). The conclusion from my research is a framework called connected leadership, which describes the critical success factors and how they inter-relate. The first factor is having senior leadership committed to being role models, which is a pre-requisite for successful transition. There are then two factors that lay a strong foundation for the transition, namely having a shared organisational purpose and vison and values-based approach to leadership behaviour. Finally there are factors that then make distributed leadership work in practice: consistently devolved decision making, an emphasis on collaborative achievement, and agility and learning. The thesis provides practitioners with insight at both the organisational and leadership role levels, based on the connected leadership model. At the organisational level, I have derived from the research certain indicators for each factor that help diagnose and plan for the introduction of a distributed leadership approach. At the leadership role level the framework provides a helpful guide to developing leadership capability and role definition. The connected leadership model represents a coherent guide for leaders to use as a template for successful transition to a more distributed, collaborative and agile organisation, which is able to compete effectively in the 21st century networked society. Academically, this thesis provides a synthesis of distributed and complexity leadership theories, as well as drawing on authentic leadership theory, in order to understand the organisational and human dynamics that influence the transition to a more distributed leadership approach. Both cases are large organisations, which means that the factor framework provides relevant insight into how distributed leadership can be effective in large and relatively complex organisations.