In an era of Covid 19, The Court of Justice of the European Union explores the extent to which the CJEU can realise a powerful role as guardian of the EU’s rule of law in a public health emergency. Drawing on an extensive literature review, The Court of Justice of the European Union argues the CJEU can realise such a role by anchoring a structured rule of law review in its reasoning when considering the exercise by the Member States of the public health derogation. Both the legal reasoning of the CJEU during the Covid 19 public health emergency and its aftermath, as well as the related challenges to the EU’s rule of law, are legally and politically of intense interest to legal academics, legal practitioners, policy makers and students.