PurposeThrough a resource-based theoretical lens, we elucidate conditions under which family business culture (FBC) amplifies the positive effects of high-performance work systems (HPWS) intensity and exacerbates the negative effects of low human capital uniqueness (HCU) on firm performance. By doing so, we answer the call for more research on the conditions under which FBC influences firm outcomes.Design/methodology/approachThe present study sampled 226 small business owners across the USA, who provided their responses to online survey questions. Hypotheses were assessed via path analysis in MPlus 8.8, using maximum likelihood estimation.FindingsFBC, HPWS intensity and HCU were positively associated with firm performance. Further, the HPWS intensity – firm performance and HCU – firm performance links were moderated by FBC. Specifically, increased levels of HPWS intensity were associated with greater firm performance when FBC was high, and firms with low levels of HCU tended to have particularly decreased levels of firm performance when FBC was low.Research limitations/implicationsConsistent with the resource-based view, firms' unique resources and competitive advantage may be tied to the extent to which they have an established FBC. High levels of FBC, which are characterized by shared values, loyalty, proud involvement and care toward the organization, can play a significant role in enhancing organizational performance. Family business leaders should prioritize cultivating an enhanced FBC alongside investments in HPWS and unique human capital.Originality/valueThis study contributes to understanding the theoretical underpinnings of FBC and its relationship with firm performance by examining FBC’s interaction with HPWS intensity and HCU. We highlight FBC as a valuable intangible resource that can enhance or diminish the effectiveness of other strategic resources in family firms, further extending the application of resource-based view theory in family business research.