Although entrepreneurship is well recognised as a crucial element in fostering economic development and growth, it is yet to be viewed as a significant force in sustainability transitions. Public policy related to the performance and growth of small businesses has, to date, paid little attention to the support mechanisms that help SMEs build capacity towards sustainable development. This paper offers a framework of pro-environmental enterprise support developed through a two-round e-Delphi study, followed by a 2.5-h virtual focus group involving 21 experts across the spectrum of business support agencies, local authorities, and EU-funded projects delivering pro-environmental enterprise support in England. The findings indicate that support for pro-environmental SME capacity building includes attention to eco-innovation, environmental strategy, environmental capability development, responsible leadership, sustainable value proposition, greening of supply chains, and clean growth skills. The study also concludes that support programmes and interventions need to be more attuned to the specifics of entrepreneurial learning; the challenges small business face in accessing, capturing, and utilising resources; and that broadening the scope and reach of pro-environmental support programmes needs to be matched by the competences of business support professionals.