The majority of developing countries still have fragmented structures and methods for managing projects, which leads to a high failure, abandonment, or collapse rate for both government and private sector projects. Due to poor project management practices, incompetence of project management practitioners, and a lack of understanding of the fundamentals of project management, there is a significant waste of scarce resources, and budget overruns and delays are common. These factors are major barriers to the advancement of project management in developing countries. Moreover, success factors are typically expressed in terms that are either general or specific to a given project. Therefore, this study aims to analyse the project manager and team competence and its mediating role for critical success factors in order to efficiently achieve project completion and improve the effective performance of road construction projects regulated under the south region construction project management directorate of Ethiopian Road Administration. The descriptive and inferential statistical methods were used to analyse the data gathered through questionnaires from 246 participants from contractors, consultants, and clients. Critical success factors were found to have a positively contributed effect on both project management personal competence and project success. Besides project management personal competence has a direct positively contributed effect on project success, it has a partial mediation role for critical success factors on project success. Besides its contribution to knowledge in pertinent areas, it helps construction companies to grow by managing such identified critical success factors.