The Hornsea Project One is likely to use Siemens turbines and is set to come online in 2019. It currently has construction approval.
Dong already owned a 33% stake in the project it bought in 2011 and has now acquired the remaining 66%.
Dong has a toltal of 2GW of offshore projects in the UK, including Gunfleet Sands, London Array and Walney.
Hornsea forms part of the 33GW Round 3 tender from 2010. Dong failed to win any of the projects at the time, although it later bought into both Celtic Array and Hornsea.
Speaking about the deal, Dong executive vice-president Samuel Leupold said: "We will now continue on our own to develop the project towards a final investment decision. The size of the project and the excellent wind conditions at the site, together with our strong focus on cost will make Hornsea One an important milestone towards the €100/MWh target.
"While the project is huge in size, it can be realised with technology which Dong masters, though no one else has ever built offshore wind on that scale so far from the coast."