Negotiators worked late into the night on Sunday to strike the accord ahead of a summit in London on Monday.
It comes after EU member countries hinted that the reset of relations was dependent on extending EU fishing access in British waters.
The security and defense pact formalizes cooperation between the two sides on matters such as hybrid warfare, cybersecurity, resilience of critical infrastructure and maritime safety.
On defense, the deal opens the way to the United Kingdom to participate in joint EU procurement programs.
Further negotiations will be required for the U.K. to access the EU’s € 150 billion SAFE rearmament programme, however, with budget contributions from London the price of entry.
Under the new deal, UK Foreign Secretary David Lammy and EU High Representative Kaja Kallas will hold a dialogue once per semester, in addition to regular exchanges on Russia-Ukraine, hybrid threats and Western Balkans, according to one of the diplomats.
EU and UK leaders are set to finalize the agreement later on Monday during a summit in London.