Intelligence institutions in post-conflict settings are often presented as neutral components of state-building, yet they frequently operate as instruments of regime survival. In South Sudan, the National Security Service (NSS) exemplifies how coercive governance is embedded within institutional design. Rather than functioning as a conventional intelligence bureaucracy, the NSS operates as a regime-preservation apparatus, whose legal ambiguity, budget opacity, and expansive discretionary powers stabilise elite rule while eroding public accountability. Situated within debates on civil–military relations, authoritarian governance, and institutional design, the manuscript examines how intelligence agencies reconstructed after civil war become central to post-conflict authoritarian ordering. Focusing on South Sudan, with comparative reference to Uganda, Rwanda, and Ethiopia, the study addresses three interrelated questions: how the NSS was designed—through its legal mandate, command structure, and resource allocation—to serve presidential political control rather than national intelligence functions; through which operational practices, including surveillance, detention without trial, intimidation, and targeted violence, it suppresses opposition and manages intra-elite cohesion within the SPLM; and how donor-supported security sector reform initiatives that nominally engage intelligence governance interact with the NSS’s actual political role, potentially legitimising rather than constraining its authority. Methodologically, the study combines legal analysis of the NSS Act and constitutional provisions, interviews with civil society actors, journalists, lawyers, and former NSS officials (conducted under strict protection protocols), comparative analysis with Uganda’s ISO, R