This article advances a conceptual view of the role of local government in global environmental governance ('GEG') and the system of transnational environmental law ('TEL'). The underlying hypothesis is that a deeper understanding of the role of local governments (global cities and smaller local authorities) is expedient as it has the potential to curb some recurring GEG failures and contribute towards improvements in the pursuit of the objectives of TEL. The Merton Rule in the United Kingdom is singled out to exemplify the potential of local government in the pursuit of shared transboundary and global environmental ideals. The Merton Rule refers to a progressive prescriptive local planning policy that requires new buildings to generate at least ten per cent of their energy needs from on-site renewable energy equipment. The broader effect that the Merton Rule has had and the understated emphasis on inter-actor support to be found in the literature on subsidiarity, are combined in three final observations: a) the notion of 'think global, act local' is challenged; b) the individual and joint potential and the capacity of cities and other forms of local government must be unlocked through consistent inter-actor support in the 'new' global context; and c) the role of local governments in GEG and TEL does not point in only one direction.