The decline of sovereignty in a globalised post-sovereignty era is much spoken of but the term has both external and internal dimensions. If what is required is a new constitutional dynamic in which the claims of popular sovereignty require a reframing of constitutional thinking, the question then is what might or could be the normative basis for a new framework of governance going forward and more specifically what might be the implications for the judicial role within that framework? Contemporary public fiduciary theory claims to offer “an interpretive theory of everything“ because it can illuminate “the salient features of the representative structure of public fiduciary relations.“ This paper considers whether a theorising of sovereignty in terms of public trust and fiduciary obligation can sustain a legitimate role for the judiciary as guarantors of environmental rights for present and future generations and if so, what boundaries are appropriate and how should they be set?