The 100 wind turbines Thanet Offshore wind farm off Thurness Point in Kent was completed in June and covers an area of almost 14 square miles (35 sq km).
The investment is conditional on the farm passing a series of assessments including its impact on wildlife. 0The bank gives long-term loans to wind power projects meeting EU policy targets.
Simon Brooks, from the EIB, said today: "The Thanet Offshore wind farm demonstrates how offshore wind can achieve economies of scale and make a significant contribution to renewable energy supply."
The 380ft (115m) high turbines can generate enough electricity for about 200,000 homes. The bank said the wind farm was an "important step" in the UK generating 15% of its energy from renewable sources by 2020 and would help meet renewable energy targets.
The funding goes to Vattenfall, the Swedish company which built the £780m wind farm. Johan Gyllenhoff, from Vattenfall, said: "We are proud to have built the world’s largest offshore wind farm, and we are very pleased with EIB long-term funding support."
It has not yet been revealed what the extra funding will be used for. The company also owns the 30 wind turbines Kentish Flats wind farm, off Herne Bay.