The editor of the Sunday Business Post, Mr Damien Kiberd, is to resign from the paper within a fortnight "to pursue other interests".
Mr Kiberd, who became a millionaire three years ago after the paper was sold to the British company Trinity International Holdings has been editor since 1989.
He will be replaced by Mr Ted Harding (35), an experienced business reporter, who has been deputy editor since last year. He has already acted as editor during periods when Mr Kiberd has been on leave.
A statement from the company said Mr Kiberd had decided that the time had come to pursue other interests.
The managing director, Ms Barbara Nugent, said Mr Kiberd had created an important new newspaper and ensured its "continuous record of editorial and commercial achievement".
Mr Kiberd's decision had been expected for some time among staff and Mr Harding was always favourite to succeed him.
The paper is recruiting new staff at present, with Mr Seβn MacCβrthaigh, editor of the website online.ie, becoming assistant editor.
Other staff have also been recruited, some from the Irish Independent.
Mr Kiberd's period as editor has seen the paper go from financial turmoil in the early days to its current position with circulation standing at a record level of 55,080.
Mr Kiberd said yesterday many superb journalists had worked at the paper in the last 12 years, but the current editorial team was the "finest yet".
Mr Kiberd is mainly responsible for the paper's strong nationalist line. He has also given strong support in his editorials to the business community, particularly small business.
Mr Kiberd helped to found the paper after spells with the Irish Press and the Sunday Tribune.