It had previously been announced that the Londonderry and Belfast Boucher Road branches were to close.
B&Q said: "B&Q has served the people of Northern Ireland for 26 years and the decision to reshape our store network in the region has been a hard one to make, however it forms an important part of our mission to reinvent home improvement for the modern age.
"This now offers over 40,000 home improvement products with the convenience of being delivered to the customer’s home or to their local store, through our Click & Collect service.
"Over the coming months, we will be focused on redeploying as many colleagues impacted by these changes as we can."
Coleraine, a second Belfast store, Newtonabbey and Newry B&Qs will remain open.