This systematic review explores the complexities of requirements gathering and budget governance in public sector and nonprofit project management. These two critical areas are central to the successful delivery of projects that serve the public good and support nonprofit organizations. The review identifies the methodologies, challenges, and best practices associated with requirements gathering, including traditional and agile approaches, and evaluates the budgeting practices that ensure effective financial oversight and accountability. Key findings reveal that while traditional project management methods continue to be prevalent, adopting agile and adaptive strategies can enhance stakeholder engagement and project responsiveness. Financial governance in both sectors is governed by stringent internal controls, audits, and stakeholder oversight, although risks such as budget overruns and mismanagement remain significant challenges. The review also highlights the importance of transparency and accountability tools in mitigating these risks. Theoretical contributions suggest a blended approach integrating agile methods within traditional frameworks, while practical implications emphasize the need for stronger stakeholder participation and real-time financial monitoring. Future research directions include the exploration of digital tools and community-led budgeting initiatives as key innovations to enhance project management and governance practices in these sectors. This review provides valuable insights for policymakers, nonprofit managers, and project managers aiming to improve public and nonprofit projects' efficiency, transparency, and outcomes.