Increasingly, organizations in the construction sector use teams to meet today's global competition and customer expectations, but they need better ways of evaluating the effectiveness of the teams. To ensure that construction teams are successful and effective, construction companies must promote, measure, and evaluate their teams' effectiveness. It is believed that creating a highly effective project team will produce high-end project outcomes that exceed standards, and, therefore, enhance overall productivity. Moreover, it is imperative for construction teams to know the contributing factors of team effectiveness in construction projects. The purpose of the study is to determine the role of team effectiveness in construction project teams on the overall construction project performance. It examines different factors that associated with team effectiveness and the relationship between the team effectiveness factors and project performance aspects. Quantitative and qualitative research methods are used for this study, which are survey and semi-structured interview. A Team Effectiveness Survey and Project Performance Survey are developed to use for data collection. The data collected was analyzed using several statistical tests, including Analysis of Variance (ANOVA) and linear regression. The results obtained from the data analysis are validated using semi-structured interview. It was found that Team Leadership is the most important factor in Project Change Management. Additionally, definitions of team effectiveness in construction project teams are developed based on the perspectives of project team members and project owners. The surveys developed are intended for assessment and evaluation of the construction project team to maintain their effectiveness level throughout the project phases. The outcomes from this study are anticipated to provide construction project teams with the ideas on the factors that need to be focused in order to improve team effectiveness on project performance aspects. Furthermore, the definition on team effectiveness from the team members and owner's point of view are developed to provide better understanding on what team effectiveness really means to different parties on a construction project.