The main purpose of the study was to determine the effect of project managers’ transformational and transactional leadership on Project Success in County governments. The study adopted explanatory research design. The target population of the study was 57 project managers in county governments of north rift Kenya. The primary data for the study was obtained using questionnaires. Data was analyzed using Pearson correlation coefficient and multiple regression analysis. The findings showed that transformational leadership (β1= 0.361, P<0.05) and transactional leadership (β2= 0.457, p< 0.05) had significant effect on project success. This implies that it is important for supervisors to understand the project managers’ situation and give them encouragement and assistance. Additionally, project managers need to be encouraged to take up the challenges and think about problems from a new perspective. There is therefore need for supervisors to ensure that the rewards offered to project managers capture their attention so that it can provide effective motivation to work towards attaining project success.