This paper portrays the effect of the Irish income tax system on entrepreneurial activity in the country. The purpose of the report was to determine whether tax progressivity has a negative effect on entrepreneurial activity. In addition, the paper aims to determine whether the elevated progressivity of the Irish tax system is hampering the performance of start-up companies. In order to do this, an extensive literature review led to arguing for the over-progressivity of the Irish income tax system, which allowed to develop a hypothesis. This hypothesis was then tested through a quantitative study which aimed to analyse the influence of income tax progressivity on entrepreneurial activity. The study was based on data from fifteen European countries, and the findings displayed a negative relationship between tax progressivity and entrepreneurial activity. Finally, the study addresses the common concern of excessive taxation among Irish entrepreneurs.