PurposeThis study aims to assess whether and how non-born-sustainable business incubators (BIs) – that is, BIs whose business model was not originally sustainability-oriented – promote sustainable entrepreneurship development.Design/methodology/approachThe study adopts a qualitative research design based on grounded theory and an interpretive approach. The analysis is developed by collecting interviews with ten Italian BIs, selected by purposive sampling and examining data using the Gioia methodology.FindingsThe results show that BIs, using various specific tools, facilitate the creation of a sustainability-oriented ecosystem. In this context, BIs help start-ups develop a purpose, a cultural mindset and business models that enable them to face the challenges of today’s competitive environment, in which sustainability has become (and will increasingly be) an essential requirement for companies.Research limitations/implicationsThis study contributes to the literature by highlighting the active role of non-born-sustainable BIs in promoting the development of sustainable entrepreneurship.Practical implicationsThis research has practical implications related to the opportunities for embedding sustainability in BIs’ purpose and defining a framework of operations and practices that can boost innovativeness while having a positive impact on the community and on the environment. Finally, findings suggest that BIs can foster cost reduction when implementing sustainability in start-ups.Social implicationsThe study suggests that BIs, as drivers of social change, could be sustained by public assistance and help from well-established firms to promote the spread of sustainable entrepreneurship culture and the success of sustainability-oriented start-ups.Originality/valueBIs have the potential to promote sustainable entrepreneurship, but this topic is still under-researched. While existing studies have examined the role of born-sustainable BIs in specific business sectors, this research is one of the first attempts to explore the role of non-born-sustainable BIs in fostering sustainable entrepreneurship.