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.

He was dubbed Knight Commander of the Royal Victorian Order (KCVO) by Queen Elizabeth during a visit to Belfast on 24 June 2014, when he relinquished his appointment as Director-General of the Northern Ireland Office.

[12] He married a Danish colleague, Lotte Knudsen in 1992 near Gers in south-west France.

Lotte Knudsen is currently Managing Director, Human Rights, Global & Multilateral Issues in the European External Action Service (EEAS) and previously held senior posts in the European Commission, including as Director for Justice Matters in the Directorate-General for Justice, Freedom and Security [14]