Appointed by Minister of Foreign Affairs Gordan Jandrokovic, Plenković worked as a State Secretary for European Integration during the Government of Prime Minister Jadranka Kosor.
As a State Secretary, Plenković also performed the duties of the political director for EU Affairs, co-chair of the Stabilisation and Association Croatia-EU, national coordinator for the Danube Strategy of the European Union and co-chairman of the duties of the international commissions (Bavaria-Croatia, Croatia-Baden-Württemberg, Croatia-Flanders).