Joe LaCumbre has decided to step down after 22 years as a worker director of the ESB and six years as deputy chairman.
Mr LaCumbre said he was stepping down for "personal and other reasons". He will be continuing to work with his union, the Technical, Engineering and Electrical Union (TEEU).
The board of the company was informed by Mr LaCumbre of his decision yesterday at its monthly meeting. His replacement on the board is a matter for Minister for Communications Noel Dempsey, although he will be expected to pay due regard to elections held by unions.
Mr LaCumbre was appointed deputy chairman in September 2000 by former minister for Public Enterprise Mary O'Rourke.
The nature of his position has been the cause of some friction at the company since then and several directors believe the role should be abolished.
Last year there was disagreement about whether Mr LaCumbre should chair board meetings in the absence of the chairman, Tadhg O'Donoghue.
The Government will now have to decide whether the role continues.
Mr LaCumbre was a key player in the recent deal on pensions agreed at the company. This deal, which involves extra contributions from the company and employees, is designed to reduce the pension liability from €511 million to about €140 million.
It was the pension issue that put Mr LaCumbre at odds with some other board directors last year.
Mr LaCumbre's demand that the pension issue be resolved before dividends payments were made to the Government created controversy.
Last year Mr LaCumbre said he had effectively been dismissed from his position when he was not asked to chair meetings and only the intervention by the Minister for Communications prevented a full scale boardroom row from breaking out.
Yesterday's board meeting voted through a deal to compensate ESB staff who are moving to the grid company, EirGrid.
Under this agreement, staff will receive €40,000 each for transferring to the new entity.
The deal was recently questioned by Mr Dempsey, but he stopped short of calling for it to be halted.
