The Competition Authority has approved the strategic agreement that will see BT Ireland transfer its consumer and small business broadband customers, as well as its voice telephone customers, to Vodafone.
The deal covers 84,000 customers and 3,000 small businesses.
Vodafone has said the deal will make it the number two player in the Irish fixed line broadband market after Eircom.
The two companies have said there will be no change in service to customers in the short term. In a statement, they said they will work closely to 'undertake a seamless migration of services'.