IT governance has become an important concern for business, receiving great attention from both practitioners and academics. Although some authors have stated that effective IT governance is crucial for any organization to achieve its corporate goals, little academic research is available that empirically supports the assumptions about the factors that determine the effectiveness of IT governance. In this sense, we proposed and examined a theoretical model that explains and predicts IT governance effectiveness, linking its domains and mechanisms. We empirically tested our hypotheses based on survey data gathered from 87 CIOs of large Brazilian companies. The results have implications about how IT governance domains and the adoption of different IT governance mechanisms can affect IT governance effectiveness, bringing implications from theory and practice.