Drawing on the resource‐based theory and institutional theory, we develop a framework to explain the processes by which the environmental strategy of small‐ and medium‐sized enterprises (SMEs) contributes to their competitive advantage. We test our assumption using data collected from 214 UK‐based SMEs in the technology sector. We find that the effects of environmental strategy can lead to development of their marketing competence, as well as research and development (R&D) competence, which ultimately contributes to superior financial performance. We also find that a reciprocal causal relationship exists between SMEs' marketing and R&D competences. Combined, we reveal the presence of a serial multiple mediation relationship between SMEs' environmental strategy and financial performance through marketing competence and then R&D competence, or vice versa. Our study offers important academic and managerial implications, and also points out future research directions. Copyright © 2016 John Wiley & Sons, Ltd and ERP Environment