ContextInvestment in information technology is associated with better business performance when its implementation is successful, but it has high costs in case of failure, especially for large software development projects, which typically have the highest failure rates. Agile methodologies emerged with the expectation of reducing the risk of software development project failure. ObjectiveThis research aims to answer the following question: What are the human-related critical success factors for agile software development projects to succeed? The research model comprises four explanatory variables (team capability, customer involvement, psychological safety, and team autonomy) and one dependent variable (success of agile software development projects). MethodA questionnaire-based survey was carried out, resulting in 177 valid responses. A Partial Least Squares (PLS) analysis was performed to test the theoretical model. ResultsThe findings indicate that team capability and customer involvement have the strongest effects on the success of agile software development projects. The results also show that psychological safety is a significant indirect success factor and that team autonomy appears to have a competing dynamic with psychological safety on the other two factors. ConclusionTo the best of our knowledge, this is the first study to examine the direct impact of psychological safety and its indirect effect, mediated by team capability and customer involvement, on the success of agile software development projects. The mediation, moderation, and direct effects are studied, offering theoretical and practical insights.