On April 1, 2024, the Ponsonby Rule, the constitutional convention that set the standard for Parliament’s role in how the UK makes treaties, turned 100. But the procedure for Parliament’s involvement in treaty-making is no longer fit for purpose. As the UK-Rwanda and CPTPPP Agreements show, the UK Parliament’s role in treaty-making must be reformed. In particular, the House of Commons must obtain the power to have a formal vote on international agreements before they can become binding on the UK.