This dissertation focuses on a small but growing group of Marxist Muslim youth activists on the Indonesian island of Java and explores the relationship between Islam and Marxism in their activism. The activists are part of Nahdlatul Ulama (NU; The Awakening of Religious Scholars), a traditionalist Sufi organisation, which was established in 1926 in light of the growing influence of Islamic Modernism and is particularly strong in rural Java. In the first half of the 20th century, NU was pitted against the Communist Party in a conflict over agrarian reform. After an alleged coup attempt in 1965, the Communist Party was banned, and alleged communists were persecuted and killed. Marxism remains largely discredited despite a resurgence among youth activists from the 1990s onwards. Since the 1990s, political Islam, has grown to increasing influence, while at the same time, debates around Islamic ethics have largely emphasised piety and private morality. NU is commonly regarded as a ‘moderate’ Islamic force, emphasising pluralism and tolerance. In this context, I examine an activist project that aims to establish a distinct form of Islamic political ethics. My thesis therefore examines an unlikely alliance between different value spheres. It focuses on FNKSDA (Front of NU members for the Sovereignty over Natural Resources), an activist movement engaged in solidarity primarily with peasants, but also fisherfolk and urban dwellers, who are faced with agrarian conflicts over natural resources with the state and corporations, for instance over the construction of a new international airport or a gold mine. Making use of NU’s influence in the countryside, they regard it as the organisation’s responsibility to support justice for their peasant members and work to convince religious authorities to stand up for them instead of siding with corporations, thereby exercising moral critique. My interlocutors were brought up in neo-traditionalist Islamic families within NU and turned to socialist thought at university. In my thesis, I examine what motivates them to mobilise theological justifications for political ends rather than becoming involved in existing Islamic social or secular leftist political activism. I show that their religious interpretation iii radically critiques modernist approaches that tend to emphasise individual piety and otherworldly salvation and that solidarity with the kaum Mustadl’afin – the downtrodden – is a central value to them. Developing a “materialist theology”, I argue, forms the basis of how activist leaders bring Islam and Marxism together through intellectual work and ethical reflection. However, as I show, in the process notions of hierarchy and religious exemplary leadership are reinforced despite an explicit commitment to equality because this work requires in-depth knowledge both in theological and philosophical matters, elevating a few knowledgeable individuals. Their exegesis guides the activism of FNKSDA and informs the practical work the group is doing. Beyond making strategic use of their authority as aspiring religious leaders, activists regard it as their ethical responsibility to make their religious tradition more progressive by endowing traditional religious practices with new meanings, even if this project entails tensions. At the same time, they maintain a broadly secular conception of politics and speak out against the increasing involvement of Islamism in Indonesian politics. Throughout the thesis, I focus on their reflexive ethical effort in bringing together Islam and Marxism, illuminating how they approach ethical challenges. The thesis argues that activists do not simply make strategic use of their religious authority to spread their political ideology but are motivated by religious belief and regard it as their ethical responsibility to critique their traditionalist Islamic organisation instead of giving up on it. Beyond reformism, their project aims at the development of a new version of progressive Islam. Furthermore, they apply religious practices such as prayers in their activist struggle alongside elements of the leftist activist repertoire. Acknowledging that there are no easy solutions for ethical dilemmas between these value spheres, activists nonetheless hold on to their ethical-political project. In light of this, I examine their moral lives as they seek to navigate reflexively between conflicting value spheres.