EirGrid, the company which manages the electricity transmission system, is to buy the company which runs the North's transmission system. The deal is worth around £30m (€37.6m).
SONI, based in Belfast, is a subsidiary of Northern Ireland Electricity, which is in turn owned by energy group Viridian.
NIE will continue to own and maintain the transmission network in the North. It says the SONI sale is in line with an agreement reached with the authorities in the North to enhance the independence of the transmission system operator.
EirGrid and SONI are already partners in the Single Electricity Market Operator (SEMO), which operates the all-island wholesale electricity market. EirGrid chief executive Dermot Byrne said the deal would build on the work being done on electricity markets in each jurisdiction.