Originally, the role of the European External Service was to represent the EU in trade negotiations and to undertake development co-operation activities. Over the years the External Service, in the form of delegations and representative offices, has also come to represent European interests in many other areas of EU activity. The development of new areas of EU action, and in particular the Common Foreign and Security Policy, has given an additional dimension to the work of these offices. Following the entry into force of the Lisbon Treaty on 1 December 2009, the role of the EU Delegation has been expanded to include duties previously discharged by the local (rotating) EU Presidency, such as conducting political dialogue and making diplomatic representations (demarches) on behalf of the EU and the High Representative of the Union for Foreign Affairs and Security Policy. The creation of the EU's External Action Service is leading to significant changes in the way the EU does business in third countries, with Member State diplomats being seconded to serve alongside EU officials in EU Delegations. 

The Delegation of the European Union to Vietnam, like the other 130 delegations and representations of the External Action Service in the world, serves the EU by:  

• Publicizing, explaining and implementing EU policy.
• Analyzing the policies of Vietnam, the country to which it is accredited.
• Conducting negotiations according to the mandates given to it.
• Exercising powers conferred on the European Community in third countries, by promoting Europe's interests as embodied in the Community policies (such as trade, agriculture and fisheries).
• Playing a key role in development assistance, a role which has expanded greatly in recent years as a consequence of the devolution policy which is a core part of the Commission's external assistance reform package. The Delegation now is not only closely involved in programming assistance but also manages projects directly in the field. 

Beyond these tasks, the Delegation represents the European Union in its relations with Vietnam, and plays an essential part in EU political, economic and commercial relations with the host country, as well as providing information on the policies and institutions of the EU. The Delegation also provides support and assistance to other institutions and actors of the EU, including the European Parliament. 

Although it has the status of a diplomatic mission, the EU Delegation does not deal with tasks of a consular nature (like issuing visas or providing tourist information), which are dealt with by the EU Member State Embassies and instead functions as an official channel of bilateral relations, be it political, developmental, economic or cultural.