This study investigates how informal religious law and emotion shaped the political mobilisation of the Islamic Defenders Front (FPI) during the 2017 Jakarta gubernatorial election, the 2019 general election, and the 2024 general election. Based on 124 speeches by FPI leaders, especially Rizieq Shihab, and semi-structured interviews with 59 supporters in Jakarta, Bogor, Lamongan, and Madura, it combines Islamist civilisational populism, sharia as informal law, and emotional mobilisation. The study argues that FPI leaders used sharia and emotion as resources of ideologisation, identification, and othering, framing the grievances of the ummah as politically binding religious duties. While FPI leaders especially mobilised anger, their supporters responded dominantly through confidence, hope, and anxiety, which they evaluated through reflection and judgement. The study contributes to the theory of religious populism by showing how informal religious law and plural emotions jointly activate populist attitudes and sustain collective political engagement across street protest, electoral politics, and grassroots moral commitment.
