So far 23 EU nations have agreed to join forces as part of a defence cooperation pact, driven by France and Germany whose leaders have long-campaigned for greater integration amongst member states.
The agreement will add yet another convoluted deal to the bloc, with some nations taking part while others do not.
The Permanent Structured Cooperation (PESCO) pact includes commitments to integrate armed forces, a boost in defence spending and the establishment of a joint HQ.
And EU bosses have set aside £4.9bn (€5.5bn) to fund research and development into new military hardware and the joint purchase of new equipment.
But so far the UK, Ireland, Denmark, Portugal and Malta have yet to sign up to the deal, which is seen by some as the next step towards a fully fledged EU Army.
After it is formally launched next month, PESCO will be another in a series of already complex relationship between some EU Member States and NATO.
British defence chiefs have previously vowed to veto any creation of an EU Army, with Defence Secretary Sir Michael Fallon saying in 2016 such a force would serve as a “rival to NATO”.
But the UK’s impending departure from the bloc has given France and Germany the opportunity to march forward with their plans.
The PESCO agreement features a commitment to “regularly increase defence budgets in real times”.
And it also includes a pledge to “increase the share of expenditure allocated to defence research and technology with a view to nearing the two percent of total defence spending”.
The vast majority of EU members do not currently meet NATO’s defence spending target of two per cent of GDP.
Currently, only the UK, the United States, Poland, Greece and Estonia are making good on the commitment.
Denmark has an opt out of all EU defence policies, however Politico has reported Portugal and Ireland are expected to have signed up to PESCO by the time it is formally launched next month.
Ahead of the approval of the plan in Brussels yesterday, EU foreign policy chief Federica Mogherini said: “It’s going to be quite a historic day for European defence.”
Asked why an EU Army is required in addition to NATO, Ms Mogherini said the proposed new defence union offered more flexibility.
She said: “Think of Africa, think of security in Africa.
The European Union is more present there than NATO when it comes to training of security forces, when it comes to the delicate link between development and security.
“We are better equipped to act in areas where there is not a purely military action that is needed, but we can also develop more our military capabilities to act to reinforce our strategic autonomy.”