The Role of Software Engineering Governance in National Digital Identity Infrastructure: Evidence from NIMC

National digital identity infrastructure represents one of the most consequential software engineering investments a government can make, affecting the digital rights, service access, and civic participation of entire populations. This dissertation examines the role of software engineering governance in the development, maintenance, and evolution of Nigeria's national digital identity infrastructure at the National Identity Management Commission (NIMC), contributing original theory on governance-performance relationships in public identity systems. A longitudinal embedded case study methodology is employed, spanning a 10-year retrospective analysis (2015 to 2025) of NIMC's NIN database and identity verification service architecture. Data sources include 40 interviews with current and former NIMC software engineers, senior managers, and policy advisers; architectural documentation analysis; incident log review; and benchmarking against identity infrastructure governance in Estonia, India, and Kenya. The dissertation develops the Public Identity Software Governance (PISG) theory, articulating how governance structure, stakeholder accountability, and technical standards enforcement interact to determine identity system reliability and security outcomes. The PISG theory identifies four governance failure modes observable in the NIMC case: accountability diffusion, standards volatility, vendor dependency lock-in, and security prioritisation reversal. Prescriptive recommendations derived from PISG theory target legislative reform, independent technical oversight, and software engineering standards mandation for government identity systems. The dissertation provides a theoretically grounded and empirically detailed analysis of governance in critical national software infrastructure. Keywords: digital identity, software governance, NIMC, Nigeria, national infrastructure