Since the mid-2000s, start-ups have increasingly become the driving force of new jobs and growth engines for advanced countries, and emerging nations are striving to vitalize start-ups through active government support policies. However, approximately 30% of start-ups shut down within two years of their foundation. Accordingly, this study determines the factors affecting the business sustainability of start-ups as based on available government support and provides suggestions to increase the effectiveness of the government-supported projects. This study conducted a survey of 273 start-ups in Korea, and empirically analyzed whether factors such as entrepreneurship, market orientation, and network affected business sustainability by using flow experience and entrepreneurial satisfaction as mediators. The results found that entrepreneurship affected business sustainability with flow experience and entrepreneurial satisfaction as the mediators, while market orientation affected business sustainability using flow experience as the mediator, and network affected business sustainability with entrepreneurial satisfaction as the mediator.