The entry of many private higher education institutions (HEIs) into the tertiary education industry in Sri Lanka has been conducive to a high degree of rivalry among competitors. Amid this rivalry, the private sector HEIs have realized the importance of designing and implementing strategically planned sustainable growth for institutions to provide value for their stakeholders. This study tested a theoretical model that includes two influencing factors– marketing mix strategy and strategic branding, and one moderating factor–competition, hypothesized to influence the performance and growth of HEI. Respondents (n = 322) from existing HEIs were surveyed to measure the key constructs. A multilinear regression supported a fit of data to the model. The study empirically revealed that marketing mix strategies designed and implemented by the HEIs do not positively influence the performance and growth of the institution. At the same time, strategic branding is a significant factor in influencing performance and growth. Moreover, the relationship between the marketing mix strategy and sustainability and the relationship between strategic branding and sustainability were moderated by the degree of rivalry that impacts the growth of the HEI. These results provide evidence to validate prior theories grounded in literature.