Brexit negotiations were always going to be incredibly tough given the complexity of issues and the deep political divides among UK citizens in the wake of the EU referendum. Theresa May’s government compounded these challenges with a poorly executed negotiation strategy: the UK government embarked on negotiations with other EU countries without a clear set of negotiating objectives; it was unable to represent itself as a unified negotiating team; it often found itself on the back foot, responding to EU proposals on both sequencing and content; and UK politicians pursued an ill-judged strategy that did not reflect the nature of the underlying negotiating problem or the UK’s relative power position. These weaknesses were the result of ongoing political divides within the UK cabinet, the wider Conservative Party, and UK Parliament. Domestic divisions impeded negotiations with the EU and ultimately led to the rejection of the Withdrawal Agreement by the UK Parliament. The Brexit negotiations are a powerful illustration of how failure by a government to effectively navigate domestic politics can derail international negotiations.