The Legal Basis for EU Security Guarantees for Ukraine
By: Sindija Beta and Katie Hetherington, PILPG, and Kerry Contini, Michal Zajda, Hanna Smyrnova, Ievgen Bidnyi, Nataliya Lipska, Marharyta Bahno, Ivan Tsios, Larysa Lysenko, Laura Zimmerman, Baker McKenzie
In the midst of ongoing developments in the negotiations to bring an end to Russia’s war in Ukraine, the question of post-war security guarantees for Ukraine is a recurring sticking point. Discussions initially centered around NATO membership and the possibility of bilateral agreements with the US and others. In recent weeks, however, there has been increased focus on whether the existing EU security and defense infrastructure can provide the necessary security guarantees to Ukraine.
Much of the discussions have focused on the EU’s capacity (military, financial, or otherwise) to provide such guarantees to Ukraine. There has been comparatively little attention paid to which EU legal mechanisms would form the legal framework for such guarantees. This blog post will identify, unpack, and assess the viability of the existing EU legal framework to support long-term security guarantees for Ukraine.
What Are Security Guarantees?
There is no uniform definition of the term “security guarantees”. In general, security guarantees are commonly recognized in international practice as commitments to safeguard and maintain the status and territorial integrity of a specific state or entity against security threats, foreign military interventions, or armed attacks. Such guarantees can be given by one or more states or by international organizations.
Security guarantees are usually divided into two categories: positive (protective) and negative (restrictive) guarantees.
Positive security guarantees constitute formal commitments to support a country or to take specific measures of assistance. An example of a positive security guarantee is the guarantees provided under NATO's Article 5, whereby an attack on one NATO member obligates every other NATO member to take action to protect the ally under attack.
Negative guarantees are formal undertakings to abstain from doing something. A negative guarantee may restrict the guarantor from taking certain actions. This type of guarantee can imply an obligation not to frustrate the agreement between the parties and a commitment by the guarantor to ensure compliance with its own obligations. An example of a negative security guarantee may include Russia’s promise not to threaten or use force against Ukraine’s territorial integrity in the 1997 Treaty on Friendship, Cooperation, and Partnership between Ukraine and the Russian Federation. Another example is the guarantee provided by the United States that it will not use or threaten to use nuclear weapons against countries that are party to the Treaty of Tlatelolco, which established a nuclear weapon-free zone in Latin America and the Caribbean.
In the context of Ukraine, a positive guarantee could involve a commitment by other parties (e.g., the current NATO member states or the EU) to provide military, financial, or other support to ensure lasting peace. A negative guarantee could include, for example, Ukraine adopting a neutral status or abstaining from joining NATO, or Russia again agreeing not to threaten Ukraine’s territorial integrity. Ukraine's concerns have been that negative guarantees will not secure sustainable peace nor the territorial integrity of Ukraine, as they do not provide assurance that, despite Ukraine’s neutral status, there will be no military action undertaken against it by Russia.
What are Ukraine’s Proposed Security Guarantees?
Currently, Ukrainian officials have not presented an official list of proposed security guarantees. The primary focus at this point, per the official website of the President of Ukraine, is to prepare “framework documents to ensure a reliable peace and lasting security guarantees” during a complete 30-day ceasefire. The President of Ukraine has previously stated that the three key conditions for lasting peace in Ukraine are security guarantees, extension of the sanctions against Russia, and control over Russian frozen assets to support Ukrainian reconstruction.
As declared by the Head of Office of the President of Ukraine, Andrii Yermak, any security agreement needs to be legally binding and contain specific terms. Security guarantees mentioned during various meetings and in public statements to date include the following:
Enhancement of Ukrainian air defense and implementation of the agreements reached at the NATO Summit in Washington.
Creation of a network of security guarantors, i.e., countries that would undertake a legal obligation to assist Ukraine in case of future Russian aggression.
Ukraine’s NATO membership. NATO has asserted that "Ukraine's future lies within NATO," yet Russia vehemently opposes Ukraine's potential NATO membership, effectively stalling any further discussions on the matter.
Ukraine’s EU membership. In the EU resolution published on March 12, 2025, the EU Parliament proposed to create a “coalition of the willing” that would assist Ukraine in achieving and enforcing a peace agreement and undertaking steps to accelerate Ukraine’s accession to the EU.
The remainder of this blog post discusses the security guarantees that may be available to Ukraine via the EU’s security toolbox.
The EU’s Security Toolbox
While NATO membership remains Ukraine’s long-term goal, Ukraine has made significant strides toward EU integration, including obtaining EU candidate status in 2022. With EU membership on the horizon, it is worth considering what defense and security commitments the EU itself can offer.
Several questions arise. What would be the legal basis for EU security guarantees? Does the current EU security toolbox provide the sufficient legal foundation for such guarantees? These questions can be answered by considering (1) the security guarantees that could be available to Ukraine once it becomes an EU member state, and (2) security guarantees that could be available to Ukraine now, without EU membership.
Security Guarantees Available Once Ukraine is an EU Member State
If Ukraine were to join the EU, the most significant legal basis for providing security guarantees would be Article 42(7) of the Treaty on European Union. Often referred to as the EU’s mutual defense clause, this article requires that member states provide “aid and assistance by all the means in their power” to any other member state that is the victim of armed aggression on its territory.
The language of Article 42(7) closely mirrors that of Article 5 of the NATO Treaty, and although the EU’s provision lacks NATO’s integrated military structure, it still constitutes a strong collective defense obligation. That said, unlike Article 5, the operationalization of Article 42(7) depends on the political will and capabilities of individual member states.
Article 42(7) of the Treaty on European Union has been invoked once in history: following terrorist attacks in Paris in November 2015, France requested aid and assistance under Article 42(7) of the Treaty on European Union from other EU member states. As stressed by France’s former President François Hollande in a speech on November 16, 2015, “all the Member States shall have the obligation to provide aid and assistance because the enemy is not just France’s enemy, it is Europe’s enemy”. In response to France’s request, EU members increased their focus on combating terrorism and provided various forms of assistance. The United Kingdom and Germany assisted in the military actions in Iraq and Syria against the groups relating to the Islamic State, while other member states became involved in various international missions, including those in Africa and the Middle East.
It should be noted, though, that the specific operation of Article 42 (7) of the Treaty on European Union is unclear. Demonstrably, France has proposed to clarify its functioning and assign an informational and coordinating role to a specific EU body. No such proposals have yet been implemented, and therefore while it could form a legal basis for security guarantees for Ukraine, its practical utility is difficult to assess.
Additionally, the solidarity clause in Article 222 of the Treaty on the Functioning of the European Union could complement Article 42(7) by providing mechanisms for mutual support in the event of a terrorist attack or natural or man-made disaster. Although this clause is more limited in scope, particularly requiring that the act triggering the mechanism is classified as terrorism, it demonstrates the broader spirit of solidarity that underpins the EU’s legal architecture.
Lastly, the EU has set up the PESCO (Permanent Structured Cooperation) framework, which is designed to deepen military cooperation between participating EU member states, promote collective defense capabilities, and foster greater strategic autonomy for the EU. Established under Article 42(6) of the Treaty on European Union, Article 46(2) of the Treaty on European Union, and Protocol No. 10 on Permanent Structured Cooperation in accordance with EU Decision (CFSP) 2017/2315, it enables participating countries to engage in joint defense projects and initiatives aimed at enhancing military readiness, interoperability, and defense integration.
Security Guarantees Available Without EU Membership
For as long as Ukraine remains outside the EU, the legal bases for EU security guarantees shift from treaty-based obligations to those found in the EU’s broader security and defense policy toolkit. Chief among these is the Common Security and Defence Policy, which enables the EU to develop and deploy civilian and military crisis management missions around the world.
Through the Common Security and Defence Policy, Ukraine has already engaged with various EU initiatives, including cooperation with the European Defence Agency and the use of the European Peace Facility to finance military assistance. The European Peace Facility, in particular, has played a crucial role in enabling the EU to provide substantial support to Ukraine since the onset of the Russian invasion. One of the most significant steps taken by the EU was the launch of the Military Assistance Mission in Support of Ukraine (EUMAM Ukraine) in 2022. The mission’s primary goal was to strengthen the capabilities and resilience of the Ukrainian armed forces, ensuring they are well-equipped to defend the civilian population and counter the ongoing aggression. These initiatives could continue to provide the basis for ongoing and deepened security cooperation.
Beyond these instruments, Ukraine could also benefit indirectly from arrangements such as the Berlin Plus agreement, which allows the EU to draw on NATO assets and capabilities for its own peacekeeping missions. While this framework is not a security guarantee mechanism in the strict sense, it provides a platform for coordination and resource-sharing between the EU and NATO, as demonstrated in past operations in the Western Balkans. In the Ukrainian context, similar arrangements could help amplify the reach and effectiveness of EU-led security commitments by utilizing NATO resources.
Conclusion
Taken together, these legal mechanisms demonstrate that the EU already has a range of tools at its disposal to provide meaningful security guarantees to Ukraine, both now and in a future scenario in which Ukraine becomes a member state. While the practical implementation of these mechanisms will depend on political will, resource availability, and broader geopolitical dynamics, the legal foundations for action are stronger than often assumed. Understanding and leveraging these existing frameworks is a crucial step toward crafting a credible and durable security architecture for Ukraine and, by extension, for the broader European neighborhood.