Keywords: Brexit, EU law, Supreme Court of the United Kingdom, Court of Justice of the EU, royal prerogative, parliamentary sovereignty, preliminary question, Vienna Convention on Law of Treaties, Sewel Convention
Abstract: The article maps how judgments of the United Kingdom courts (Miller I) and the Court of Justice of the European Union (Wightman) intervened in the Brexit process. Formally, the judicial intervention limited itself to the interpretation of the UK constitutional law (royal prerogative, parliamentary sovereignty) and the EU law (article 50 TEU, relation between the EU and international law). However, both judgments also had a broader impact on the political context of the Brexit process, the parliamentary control of the Brexit Agreement negotiation. Judicial intervention(s) thus not only clarified some aspects of the UK constitutional law and the EU legal order but also decreased the predictability of the Brexit process.