David O'Sullivan (born 1953) is an Irish civil servant who served as the Ambassador of the European Union to the United States from 2014 to 2019.
Prior to his post in the United States, he was the Chief Operating Officer of the European Union's diplomatic service, the European External Action Service (EEAS).
He has held a number of high level positions including Chief of Staff to Romano Prodi and Secretary-General of the European Commission between June 2000 and November 2005.
From 2005 to 2010, he was Director General for Trade.
In 2010 he was appointed as Director General for External Relations with the responsibility of setting up the EEAS and was appointed the Chief Operating Officer on 1 January 2011.