Mr Griffiths has been at ITV since September 2008, and has been credited with leading a turnaround at the company.
ITV, which plays host to hit TV show Love Island, is gearing up to announce an update on its strategic review next month.
Since January, ITV has been headed up by Carolyn McCall, the first female chief executive of the media firm.
She said Mr Griffiths had helped refresh the company’s strategy, and will continue to work on implementing it while ITV looks for a successor.
Sir Peter Bazalgette, chairman of ITV, said: “Ian has been a key part of the management team that transformed ITV’s performance.
“The strategy that Ian helped develop and deliver has created a strong platform for our future success and delivered real value for shareholders.
“On behalf of the board and our shareholders I would like to thank Ian for all he has done for ITV.”
In the first quarter of the financial year, ITV’s external revenue was up 5 per cent to £772m.
Mr Griffiths said: “I am immensely proud of everything that we have achieved at ITV, not least in keeping the business together through the financial crisis and then delivering strong shareholder returns from 2010 onwards.”