Denis O'Brien has increased his interest in Independent News and Media to 29.9%.
The announcement was made in a regulatory filing to the Irish Stock Exhange.
This is the maximum that he can own without triggering a full bid for the company.
O'Brien was already the largest shareholder in the media group.
He consolidated his control over the company last month when rival Gavin O'Reilly stepped down as chief executive.
Mr O'Reilly's departure brought to an end his family's 30-year control of Ireland's largest media company and ended years of squabbling between Mr O'Brien and the O'Reillys.
Minister for Communications, Energy & Natural Resources Pat Rabbitte said the Government's commitment in respect of ensuring that there is both diversity of content and diversity of ownership in the media remains in place.
Reacting to questions about Mr O'Brien's increased shareholding in independent news papers Mr Rabbitte says Mr O'Brien was still short of the threshold in terms of making a bid for ownership in that sense.
"The existing law on ownership applies until new ownership laws are put in place, and I would hope that can happen as soon as possible," Mr Rabbitte said.