After the resignation of Jonathan Hill as the British European Commissioner and European Commissioner for Financial Stability, Financial Services and Capital Markets Union in the aftermath of the Brexit referendum, Prime Minister David Cameron nominated King to replace him. On 2 August 2016, European Commission President Jean-Claude Juncker announced his intention to allocate the new portfolio of Security Union to King. King would work under the supervision of First Vice-President Frans Timmermans. The European Parliament confirmed his appointment on 15 September 2016, and the Council of the European Union did so on 19 September 2016. With the United Kingdom's withdrawal from the European Union on 31 January 2020, he was the last British official to hold a position and portfolio within the European Commission.