McGreevy will manage advertising and marketing in her new role, as well as maintaining her existing responsibilities for circulation and editorial cost management.
She brings 18 years of experience in the newspaper industry to the role, 15 of these with Mirror Group, where she first worked for sales in the circulation department. She was promoted to circulation director in 2001.
Richard Webb, managing director at MGN, said: "Joanne's skill and experience will help build on the success of our Irish operation and I am delighted she has taken up this position."
The company also announced four further promotions.
Joanne Friel, the former promotions manager in Ireland, is to become marketing and promotions manager. She will be responsible for developing the overall marketing and promotional strategy for the Mirror Group business in Ireland.
Mark Whyte, the marketing and sponsorship executive, will take the role of marketing services manager, working alongside Friel.
Other promotions include Jonathon Eakin, from agency manager to Northern Ireland advertising manager; while Alan Kelly, previously sales manager for the ROI, is to become circulation manager in Ireland.
Separately, David Montgomery, former chief executive of Mirror Group Newspapers, yesterday agreed to buy Wegener, the Dutch regional publisher, for up to €806m (£548m), through his investment vehicle Mecom.
The acquisition of Wegener, the largest publisher of regional newspapers and free door-to-door papers in the Netherlands, would create a larger newspaper business than Trinity Mirror.
Mecom, which already owns about 20% of Wegener, publisher of newspapers such as the Eindhovens Dagblad, is offering around €18 (£12) a share to Wegener's shareholders.