The analysis of human resources and sustainable innovation through organizational variables is useful, albeit limited, for predicting complex interactions for sustainability development in small and medium-sized enterprises (SMEs). This paper seeks to overcome this limitation, proposing three models with variables at two levels, namely, for the development of creativity (individual level) and sustainable product innovation performance (organizational level) and sustainability development. Theoretical models are tested using the Structural Equations Model. It is posited that knowledge, motivation, and relationships (individual level) may be predictors of creativity. In addition, creativity is analyzed as a mediator between human resources and sustainable product innovation performance. In this way, it is easier for SMEs to detect on which aspects of HR they should place greater emphasis for sustainable product innovation performance (PIP), with the purpose of reducing the ones associated with the Covid-19 crisis and obtaining a sustainable world. Information was obtained through an online questionnaire involving a sample of 245 certified innovative Spanish SMEs. The results support major findings: (a) knowledge, (b) motivation, and (c) relationships have a positive impact on creativity; (d) the three models hold that creativity fully mediates human resources and sustainable product innovation performance. The paper contributes to the literature on the human resources and sustainable product innovation performance by adopting a multidisciplinary approach, as well as by analyzing variables on two levels, measuring the most internal aspects of employees (wishes, emotions, ideas, or feelings), and explaining the mediating role of employee creativity.