Mark Sedwill, Baron Sedwill of Sherborne KCMG FRGS FIoD, is a British diplomat and former civil servant who served as Cabinet Secretary to Prime Ministers Theresa May and Boris Johnson and Head of the Civil Service from 2018 to 2020, and as National Security Adviser (2017-20). He was previously the UK’s Ambassador to Afghanistan (2009-10), NATO Senior Civilian Representative in Afghanistan (2010-11) and Permanent Secretary at the Home Office (2013-17). He joined the Foreign & Commonwealth Office in 1989, serving in Egypt, Syria, Iraq, Cyprus, Jordan and Pakistan.