The EUR 2.4 billion development is using Siemens' 3.6MW turbine. German developer RWE is hoping to have it fully operational by the end of this year.
A2Sea's Sea Worker vessel installed the final turbine at the site in Liverpool Bay, 13 kilometres off the North Wales coast.
All the turbines have now been installed using A2Sea's Sea Worker and Sea Jack jack-up vessels. Work is still ongoing to fit the array cables.
When it is completed, it will become the world's second largest operational offshore development behind the 630MW London Array.
Gwynt y Môr, owned by German developer RWE Innogy (60%), energy supplier Stadtwerke München (30%) and technology giant Siemens (10%), comprises 160 Siemens 3.6MW turbines.