This paper explores the role of ideology on militant Islamist groups in Egypt. Starting from the premise that ideology should be considered both a dependent and an independent factor, this research investigates the operationalisation of the separation between ideational and material explanations in the study of the praxis of militant groups. First, it briefly reviews common studies of Islamist militancy and deplores the unproductive divide between partisans of an overstated stress on ideology, defined by a limited corpus of textual sources, and their contenders who disprove and reject ideational factors and rather favour a focus on other macro, meso or micro parameters. Thereafter, it identifies the acknowledgement of this stalemate in the literature and illustrates some attempts to bridge the gap between these studies. Then, it presents a new theoretical approach based on the use of process tracing and social movement theory. This new perspective postulates that ideology encompasses central and secondary components that co-exist in a militant group and asserts that the ideological evolution of a group has to be investigated and deciphered through the unfolding of its long terms ideological commitments. It consequently proposes that the later have to be analysed through textual analysis associated with in-depth interviews of the protagonists who wrote these key texts. These interviews are deemed crucial to uncover the formation of a textual consensus and to relate the text to broader macro and organisational factors. This approach therefore allows for a more acute understanding of circumstantial short-term ideological compromises and long term commitments. This study is applied to al-Jama'ah al-Islamiyah (the Islamic Group) and Jama'ah al-Jihad (the Jihad Group) in Egypt and is based on extensive interviews with leaders and members of both groups. It illustrates this new theoretical approach through the focus on these groups' respective position on violence and democracy from their inception to the post-2011 Egyptian uprising. This research is important to both practitioners and academics and ought to inform future policies and research. Even if the present study is centred on violent groups, the same approach can indeed potentially be applied to other non-violent Islamist movements.