The language and practice of Marine spatial planning (MSP) is typically associated with state-led multi-sectoral planning efforts. Yet in countries like India, where the government is not yet promoting MSP, ocean space has already been divided using principles and practices that are characteristic of MSP elsewhere in the world. Instead of being initiated by the state, these MSP-like processes are initiated by international agencies when industries seek large-scale development of India's marine ecosystems. Although intended as an inclusive, holistic process to plan industrial development, this assemblage of MSP technologies, processes and practices mandated by international corporations produces a particular power relation through its rejection of local knowledge and insistence on data, for instance, in the form of discrete, geo-coded polygons. This paper argues that this form of MSP produces an ontological politics, despite emerging from seemingly rational, post-political and technocratic processes. Engaging with such politics is increasingly possible with access to geographical information systems and this, therefore, provides a novel space in which to engage in political struggle. The case of externally mandated MSP in India demonstrates that non-state actors can initiate MSP and therefore, opens the possibility for fishing communities, as non-state actors, to directly engage with the assemblage of practices that produce MSP.