MHI Vestas will supply 40 V164-8MW turbines that have been uprated using Vestas' 'power mode' option to produce 8.25MW per turbine.
The contract includes a five-year servicing deal, with installation to commence in 2017 and be completed in 2018.
Blades for the V164 turbines will be made at MHI Vestas' Isle of Wight facility off the UK's south coast.
Dong's 330MW Walney Extension West will be built alongside the 329MW Walney Extension East project.
Siemens will supply 47 SWT-7.0-154 turbines to the 'East' project in a deal that was confirmed following the project's final investment decision in October.
Both manufacturers were named preferred suppliers in Q1 2015.
Dong split the 659MW project into two phases because the site has two distinct areas with differing features.
"This will allow us to optimise the site and create two separate phases of the project. This, with the flexibility afforded to us through the phased contract for difference (CfD) agreements, enables us to exploit the opportunity to develop the project using different technology," said a Dong spokesperson.
The Walney Extension was handed a final investment decision-enabling CfD subsidy by the UK government in April 2014 and was approved in November 2014.
Walney Extension is located 19km off the UK's west coast in the Irish Sea beside the 367.2MW Walney development, completed by Dong in 2012 and powered by 3.6MW Siemens turbines.
Danish vessels firm CT Offshore has won the contract to install the project's inter array cables across both phases.