The merger between Lakeland Dairies Co-operative Society and LacPatrick Co-operative Society has been approved by both the UK's Competition and Markets Authority and the Irish Competition and Consumer Protection Commission.
Both authorities said that competition would not be adversely affected as a result of the merger and both cleared the transaction unconditionally.
The regulatory authorities' clearance was the last significant hurdle for the merger to go ahead.
Last October, the Lakeland and LacPatrick shareholders voted 97% and 96% respectively in favour of forming one of the largest dairy processors in Europe.
The new society will be called Lakeland Dairies Co-Operative Society Limited and will be the second largest dairy processor on the island of Ireland.
It will have a cross-border milk pool of 1.8 billion litres, produced by 3,200 farms from 15 counties.
The new co-op will have a combined annual turnover in excess of €1 billion, which is said will create internationally competitive scale while ensuring efficient costs of operation.
Lakeland Dairies was established in 1990 through the merger of Killeshandra Co-operative and Lough Egish Co-operative.
LacPatrick was set in 2015 following the merger of Ballyrashane Co-op and Town of Monaghan Co-op.
Michael Hanley, CEO designate of the new Lakeland Dairies, said he was very pleased to have reached the conclusion of this process which is now a starting point for future significant progress.
"We are energised and ambitious to create strategic advantages in an intensely competitive market environment where we intend to ensure the best possible realisation of the benefits of this merger for our members and for all of our customers around the world," he added.