Despite the burgeoning interests in the environmental strategy, there is a limited understanding of how human resource slack drives sustainable innovation and environmental performance. This paper contributes to filling this gap by examining the effect of human resource slack on sustainable innovation and its impact on environmental performance. Besides, this paper investigates the contingent effects of intangible resource advantage on this relationship. The hypotheses are tested using data from 301 small and medium-sized enterprises in Ghana. The results suggest that human resource slack positively relates to sustainable innovation and this relationship is moderated by intangible resource advantage. Also, we find that sustainable innovation mediates the relationship between human resource slack and environmental performance. The insights from our paper provide a nuanced understanding of the relationships among human resource lack, sustainable innovation, and environmental performance. Implications for theory and practices are discussed.