Gavin O'Reilly has resigned as chief executive of Independent News and Media.
He will be replaced by Vincent Crowley, the current chief operating officer of INM and former head of its Irish operations.
It is understood he cited recent shareholder activism as becoming a distraction from the running of the company.
Mr O'Reilly had come under pressure in recent months from two of INM's largest shareholders; businessman Denis O'Brien and financier Dermot Desmond.
Both men, who own just over a quarter of the company's shares between them, were expected to vote against Mr O'Reilly's reappointment as a director and chief executive at INM's annual general meeting in June.
This morning it also emerged an anonymous buyer purchased 13 million shares in the group, which equates to 2% of the company.
A meeting of the board of INM took place this afternoon following the intense pressure on Mr O'Reilly, after which his resignation was announced.
The company's shares have fallen by more than 60% in value over the past year.
Although Mr O'Reilly said as recently as last month that he retained the support of the majority of its shareholders, it is understood he felt the issue of his leadership and the criticism from Denis O'Brien and Dermot Desmond was becoming a distraction.
INM shares closed 6.5% higher at 24c in Dublin this evening.