O'Reilly, who is the largest shareholder in IN&M with around 28.5% of the group, has worked for the company for the past 36 years.
His son Gavin O'Reilly, the current chief operating officer, has been appointed to succeed him as chief executive. He joined IN&M in 1993 and has worked as chief operating officer for eight years.
Dr Brian Hillery, chairman of IN&M, said: "Tony's retirement marks one of the most remarkable executive careers in Irish history.
"Tony has been a significant business leader for more than 45 years and has been a key figure in the making of modern Ireland.
"Tony can be immensely proud that from modest beginnings 36 years ago, he has helped to build a truly global communications business.
"When Tony first invested in a local Irish newspaper operation back in 1973, it had a turnover of €12m. From that starting point, he immediately applied -- with his colleagues -- his flair, vision and enormous energy to create a €1.5bn worldwide communications group.
IN&M has named O'Reilly as president emeritus to recognise his contribution to the group.
O'Reilly said: "It has been more than three decades since I first became involved with Independent and in that time it has been my pleasure to have worked with a range of highly talented and hugely committed directors and colleagues.
"My appreciation of them is undiminished by time. Together, we have expanded this Irish newspaper group and enshrined a fiercely independent editorial policy that is widely respected across the world.
"As the largest shareholder, I will continue to support their legacy and this wonderful group in the furtherance of its strategy."
IN&M is also set to reduce its board's membership from 17 to 10 members over the next three months after indicating its intention to do so at last year's annual general meeting.
New members are being appointed, as others retire.
The new 10-member board will comprise of:
- Dr Brian Hillery, chairman.
- Gavin O'Reilly, chief executive.
- Donal Buggy, chief financial officer.
- Ken Clarke, Baroness Margaret Jay, Brian Mulroney and Frank Murray as non-executive directors.
- Leslie Buckley, Paul Connolly and Lucy Gaffney have also been appointed onto the board with immediate effect.
Hillery said: "I want, on behalf of all of our shareholders, to pay a special tribute to each of the directors who will be retiring or not seeking re-election at the AGM.
"I also want to welcome Leslie, Paul and Lucy onto the board; their arrival signals a positive and constructive engagement in the affairs of the company."
IN&M said Denis O'Brien, the group's second largest shareholder with 26%, supported the changes to the board.
O'Brien had been labelled a dissident shareholder by IN&M following his calls for major changes at the group including the sale of its loss-making flagship titles The Independent and Independent on Sunday.
Hillery said: "We are working with Denis towards a common goal in the interests of all shareholders which will enable us to better navigate the uncertainties of the current world economic turmoil and more successfully enhance the group's future prospects."
IN&M is set to release its preliminary 2008 results on April 24.