Stakeholder behavior and stakeholder management are necessary success essentials within project portfolio management (PPM) success. This empirical study of 87 well known software houses of Lahore, were organizing projects in portfolios investigated the effect of engagement of stakeholder's engagement on project portfolio management success. Study mentioned that the effect of stakeholders was phase-peculiar and that role clarity affected the nature of the relationship between the stakeholder's engagement and project portfolio management success as a moderator. Data analysis was employed by Pearson correlation and Step wise Hierarchical Regression. Results described that stakeholder's engagement had insignificant effect on the PPM success, but with moderating effect of role clarity internal stakeholder's engagement show strong and highly significant effect on the PPM success. Results also mentioned that external stakeholder's engagement had significant effect on the PPM success, furthermore moderating effect of role clarity also keep significant relationship between external stakeholder's engagement and PPM success. This study enriches project research by applying stakeholder theory.