The Swedish firm will spend just more than €1bn in the project, which is expected to be online in 2018.
Vattenfall won the bid for the concession to construct the wind farm in February 2015.
In June 2015, MHI Vestas Offshore Wind had been selected as preferred supplier of turbines, of the V164-8 MW model, for the project.
Vattenfall and MHI Vestas Offshore Wind have entered into a conditional agreement regarding the turbines delivery.
Vestas said it will issue another statement once there is a firm and unconditional order.
When completed in late 2018, the Horns Rev 3 wind farm will power about 400,000 Danish homes and reduce about 570,000 tonnes of carbon dioxide and 13,000 tonnes of sulphur dioxide emissions annually.
Vattenfall president and CEO Magnus Hall said: "Horns Rev 3 is an important part of Vattenfall´s ambitions in the field of wind and particularly on our focus on offshore wind farms.
"Horns Rev 3 also gives a clear signal to the world around us that Vattenfall´s strategy is to make new investments in renewable electricity generation and to grow in wind.
"Vattenfall supports the transition to a totally renewable energy system and takes up the challenge, in spite of current low electricity prices and excess capacity."
Image: Vattenfall will begin construction work for the Horns Rev 3 offshore wind farm in Denmark. Photo: Courtesy of Heidi Lundsgaard.
