Iberdrola has commissioned the New England Clean Energy Connect transmission network through its US subsidiary Avangrid.
Iberdrola said the 233-kilometre high-voltage line is now carrying hydroelectric power from Quebec with a 1200MW capacity supplying nearly 10% of electricity consumed in Massachusetts.
The company added that the project began in 2018 and has been completed after securing all federal and state permits.
The $1.65bn line has regulated 40-year contracts with Massachusetts distributors and Hydro-Québec.
NECEC incorporates HVDC converter technology and two 300MVAR STATCOMs installed at the Buxton substation in Maine.
The project will contribute hundreds of millions of dollars to community initiatives and programmes.
Iberdrola said around 20,200 hectares have been secured to protect regional ecosystems.