Germany and France are leading the charge for a new defence union, which aims to cement EU unity after Brexit.
The campaign for a European defence union stretches back to the 1950s, although the movement has stuttered in the decades since.
But EU officials are now celebrating as progress accelerates with the support of Brussels chiefs Jean-Claude Juncker, Guy Verhofstadt and Michel Barnier.
One unnamed official quoted by Reuters news agency said today: “We’ve never come this far before. We are in a new situation.”
EU foreign and defence ministers signed the new pact at around 10.30am GMT. EU leaders will then officially back it next month to make it EU law.
Federica Mogherini emphasised the importance of today’s agreement this morning.
The EU’s High Representative for Foreign Affairs and Security said: “It’s going to be quite a historic day today for European defence.”
The pilot stage will include a system to spot weaknesses across EU armed forces, while a multi-billion-euro fund to support the pact is still under negotiation.
It is just the latest step in the march towards an all-out EU army, with a military headquarters already approved and proposals to purchase military equipment being considered.
Long blocked by Britain, which feared the creation of an EU army, defence integration was revived by France and Germany after last June’s Brexit vote.
It follows years of spending cuts that have left European military forces short of vital assets.
Already the majority of EU members do not meet Nato’s defence spending target of 2 per cent, with only Poland, Greece and Estonia budgeting for the amount.
Britain, and the US are the other two nations meeting the target.