Mr Jackie Gallagher, who has worked as special adviser to the Taoiseach, Mr Ahern, since 1994, has joined Fleishman-Hillard Saunders as director of corporate relations.
Before joining Mr Ahern's back-room team, Mr Gallagher spent seven years with The Irish Times, as a senior business reporter and later as industry and employment correspondent.
His appointment is the latest in a series at the public relations firm as it seeks to build its financial and corporate communications business.