The High Court has rejected an appeal against the North-South Electricity Interconnector.
Business group Ibec has welcomed the ruling in favour of An Bord Pleanála.
The group says this should pave the way for the commencement of work on the "long-delayed but vital" interconnector.
Speaking after the ruling, Ibec CEO Danny McCoy said: "The major competitive challenges created by Brexit make construction of the North-South Interconnector more relevant than ever before.
"Sufficient electricity supply is essential for growing our economy and is a significant factor in ensuring we seize the inward investment opportunities that will arise in the next few years.
"It is worrying, to say the least, that Northern Ireland is facing an electricity supply deficit by 2021, if North-South electricity flows are not safeguarded.
"The Interconnector can address this problem by strengthening the electricity grid, reducing the risk of power shortages and blackouts, all at a lower cost to users", Mr McCoy added.
EirGrid also welcomed the decision to uphold the planning approval for the southern element of the project.
John Fitzgerald, director of grid development and interconnection at EirGrid, said: "The North South Interconnector is undoubtedly the most important infrastructure scheme on the island today and will help deliver very real benefits to domestic and commercial customers.
"We look forward to moving on to the next stage of the project, in particular engaging with landowners in Meath, Cavan and Monaghan who are directly affected by it."
The proposed construction would see 400 pylons built on a route from Meath to Tyrone.
When Eirgrid submitted the plans to An Bord Pleanála, more than 900 objections were lodged.
Landowners and residents raised numerous concerns about the project during a 12-week oral hearing into the development in 2016.