Declan Costello was born in Galway, Ireland in 1967.
He has a Degree in Economics from Trinity College Dublin and a Masters' Degree from the College of Europe in Bruges.
He joined the European Commission in 1991 and has worked since then in the Directorate General for Economic and Financial Affairs (DG ECFIN) working on issues such as the launch of the euro, the Stability and Growth Pact (SGP) and subsequently European Semester 2020 strategy.
From 2012 to 2014, he was acting Director for Resources and Communication in DG ECFIN.
From May 2014, he has been the European Commission's Mission Chief for Greece. During this period, he led the negotiations with the Greek authorities on the design and monitoring of policy conditionality underpinning the EFSF and subsequently ESM stability programme for Greece. He was also active in the discussions that led to measures being agreed by the Eurogroup in 2016 and 2018 to ensure the sustainability of Greek public debt.
In August 2019, Mr Costello was nominated Deputy Director General in DG ECFIN.