The project comprises 51 Siemens SWT-3.6-107 turbines that when fully operational will have a generating capacity183.6MW.
When combined with the 183.6MW Walney 1, which became fully operational in July, Walney will be the largest offshore wind farm in the world, with a total capacity of 367.2MW.
Walney's ownership comprises Dong Energy (50.1%), SSE (Scottish and Southern Energy) (25.1%) and OPW (24.8%), a company jointly owned by Dutch pension administrator PGGM and Ampère Equity Fund (managed by Triodos Investment Management).
Dong Energy is the leading partner in the construction and operational phases of both projects, and the company's chief executive Anders Eldrup said that Walney 2 was the fastest ever installation of an offshore wind farm.
"We developed our techniques for faster and more cost efficient installation methods in the challenging conditions in the Irish Sea," said Eldrup.
"This is an important step in the continuing drive to reduce the cost of construction of offshore wind farms."
The UK government last month launched a taskforce to investigate cutting the cost of offshore wind.