EirGrid's €80m Laois-Kilkenny reinforcement project has been approved by An Bord Pleanála.
The decision to grant planning permission with conditions has been met with shock and disappointment by opponents of the plan.
EirGrid said the Laois-Kilkenny Reinforcement Project is a necessary enhancement of the transmission system for the midlands and southeast.
The project consists of a new 110/38kV substation at Ballyragget in Kilkenny and a new 400/110kV substation at Coolnabacky in Laois, with a 26km line connecting the two stations.
Coolnabacky will then take new connections from the existing Moneypoint-Dunstown and Athy-Portlaoise lines.
The Ballyragget to Kilkenny line will also be upgraded.
Campaigners in Co Laois believe the planned substation at Coolnabacky is too large and they fear the area will become a major electrical hub.
Ratheniska, Timahoe and Spink Substation Action Group spokesman Colm Fingleton said: "We are all kind of stunned with the decision.
"I think it is an outrage, it's like they never heard our concerns."
However, he admitted there had been a general consensus among action group members that the decision was a "foregone conclusion".
Members of the group are going to hold a meeting in the coming days.
"We are going to consult and see where we go from here, but it's certainly not over," Mr Fingleton said.
Labour Senator and Timahoe resident John Whelan was equally displeased at the decision.
"Along with the rest of the community I am shocked and devastated by this ruling," he said.
"It's as if the consultation process and the six-day hearing never took place at all. No wonder communities are so cynical of this pointless process."
He described the consultation as "a charade with no real engagement".
Mr Whelan added: "Where is the undergrounding that EirGrid boast of in their expensive adverts which the taxpayer is paying for?
"The entire process is a farce and a fraud from beginning to end.
"I, for one, will not be relenting in my outright opposition to this Grid 25 EirGrid gravy train being funded to the tune of €4bn by the taxpayer for no need."
"The Ratheniska so-called sub-station is a 17-line hi-voltage renewal energy hub and has nothing whatsoever to do with power supply to Kilkenny.
A report from an An Bord Pleanála inspector concluded many of the concerns expressed in both written submissions and during the oral hearing had been "overstated".