Improvement of road infrastructure was identified by the Kenyan Government in its Vision 2030 as one of the critical drivers of the country’s economic transformation. Whereas the Government has continued to invest heavily towards road construction, the challenge of delays in completion of road construction projects and cost overruns continue to hamper accelerated road improvement in the country. More than 50 percent of all road construction projects in Kenya are completed late with significant cost overruns. The study sought to evaluate the critical factors and their influence on performance of road construction projects in Kiambu County, Kenya. The research adopted a descriptive research design. Data was collected from a census of 9 road construction projects in the county. The target population was the 158 officers, who worked in the Kiambu regional offices for KURA, KeRRA, KeNHA and the county’s Ministry of Public Works as well as representatives of the contractors undertaking the road construction projects that were ongoing as at the time of the study. A stratified sample of 82 respondents was chosen from which data was collected using self-administrated questionnaires. The collected data was analysed using descriptive statistics and inferential statistics. Inferences of the study were made using regression analysis. The findings of the study were presented in the form of charts and tables. The study found out that performance of road construction projects in Kiambu County, Kenya was affected by project funding, contractor capacity, project planning and project monitoring and evaluation. It was therefore recommended that financiers of road construction projects need to ensure that contractors with strong capacity are selected. In addition, adequate and timely financing of road construction projects ought to be undertaken as well as regular project monitoring and evaluation. Moreover, it is imperative for proper project planning to be undertaken for successful performance of road construction projects. Stakeholders’ involvement however was not found to have any significant influence on performance of road construction projects.