Project implementation is one of the key activities in the process of ensuring development. In public institutions, the challenges in project management are particularly evident. Organizational inflexibility and an inability to adequately evaluate work are particularly emphasized, often creating problems during project implementation. These challenges become even greater if the financing of the project is planned with EU grants or other financial instruments that require great precision and thus exceptional project management skills. This document will present an effective project management model, as well as programs and portfolios in regional self-government units. A methodology has been developed to encourage the transformation of public systems from rigidly functional to project systems. The methodology was tested in Primorje-Gorski Kotar County, Republic of Croatia. An analysis of the quality of implementation of twenty projects has been carried out: an analysis of the final results of ten projects in which the methodology has been applied and of ten projects in which the methodology has not been applied. After conducting empirical research and analysis, the quality of the proposed model was proven at all levels of governance within the public sector. By applying this methodology, significant advances can be made in the quality of realized projects while ensuring the realistic dynamics of this realization and rational financial costs.