CIP acquired the project in August 2016 when it bought developer OffshoreMW from US private equity firm Blackstone.
OffshoreMW won the lease to the 675 square kilometre site in January 2015 after a federal auction process. It won with a $166,886 bid.
CIP will continue to hold the remaining 50% stake of its project, with one of its funds holding 25% of that.
Avangrid – 81.5% owned by Ibedrola – also owns the up-to-1.5GW Kitty Hawk lease area off North Carolina following another federal auction in March 2017.
"Our equal partnership in this effort demonstrates the strong commitment we've made to execute our growth strategy and expand our wind portfolio across the US," said Avangrid CEO James Torgerson.
"When you look at our longer term position with the Kitty Hawk off-shore lease in North Carolina and factor in this more immediate off-shore opportunity in Massachusetts, combined with our family of company's extensive experience and knowledge, you recognise we are well positioned to grow this sector in the US."