The interconnector is around 260 kilometres in length and has the capacity to carry 500 megawatts of electricity between Ireland and Britain, and enough energy to power 300,000 homes.
It is the largest single piece of energy infrastructure to be built here since the Ardnacrusha Hydroelectric power station was opened in 1929.
It will allow electricity to be bought and sold between the two countries.
Eirgrid, which was in charge of delivering the project, said it had come in on time and below its €600m budget.
The semi-state company said the connector will help maintain the security of supply and encourage the development of renewable energy sources here.
Taoiseach Enda Kenny is expected to attend today’s official opening ceremony, with the interconnector beginning commercial operations on 1 October.