The new 735-kilovolt power line will go from the Lac-Saint-Jean region, about 200 kilometres north of Quebec City, to Montreal.
''It's been 20 years since the last time we built such a line," the premier told a news conference, adding it would create jobs in several regions.
''It is a necessary project. It is not only good for the stability of the network. It is good for Quebec as a whole.''
Couillard told a news conference Quebecers will be happy to see construction of the $1.4-billion line go ahead over the next 18 months.
The line has faced opposition from a citizens group as well as a number of municipalities, environmental groups and farmers.
The province's environmental review board also did not give the so-called Chamouchouane-Bout-de-l'Isle project its approval.
But the plan did get the nod from Quebec's energy board and the agency that oversees protection of agricultural territory.
An information sheet provided by Hydro-Quebec said 300 meetings and exchanges have been held with the communities involved since 2010.
It said that, in light of concerns that were expressed, the utility proposed a new route located to the west of the initial one.
Hydro said the project will considerably reduce electricity losses, reinforce the main transmission network and increase the network’s operating flexibility.