User innovation is a new economic paradigm that has the ability to create a new engine for social and economic development. Furthermore, many users are not limited to their role as a user but evolve into business starters, thus becoming user entrepreneurs. This study aimed to reveal the important factors of successful user entrepreneurship by closely investigating two successful Korean user entrepreneurship cases. Based on this study’s findings, the importance of an entrepreneur’s caliber and networking ability was found. An entrepreneur’s innovation ability from expert knowledge and great familiarity and experience with the business as a user coupled with a strong will to entrepreneurship was the most important success factor at the early stage. In further developing user innovation technologically and commercially, the most important factor was an entrepreneur’s networking ability that can give access to complementary assets for successful development and commercialisation. With this, the innovation community—composed of related users and producers—has played a crucial role in the successful entrepreneurial process.