Businessman Mr Joe Burke was made chairman of the Dublin Port Authority after he requested a place on the board from the Taoiseach, Mr Ahern, it emerged yesterday.
The appointment was made by the Minister for the Marine, Mr Fahey.
Defending the appointment, Mr Ahern insisted he had not asked that Mr Burke, a long-standing friend, be made a chairman of the port, the biggest in the country.
"He made me aware that he would possibly like to be on the board. I certainly did not lobby for him to be chairman. But he got that position on merit because he is a very committed member of Dublin Port," Mr Ahern told The Irish Times.
On Sunday night, a spokeswoman for the Taoiseach said that Mr Ahern had been "routinely informed of the appointment" by the Minister for the Marine before it was made two weeks ago.
Facing accusations of political cronyism from Fine Gael and Labour, Mr Ahern said: "I must say that I am very disappointed that that would be said about Joe Burke."
Mr Ahern said the businessman and builder had "a number of attributes more" than he had, when he himself sat on the port and docks board.
"While I was most anxious to see him on the board because he has a huge interest in the board and he is a friend of mine, his nomination as chairman by the Minister for the Marine was because of his knowledge.
"Joe Burke has a huge interest in the port. He has always had a huge interest in the port. His wife's family is from the port. He lived in the port. He was always a great protector of people in the port," Mr Ahern said.
"I know this for a fact: the people who served with him on the board believed he was an excellent member of the board," said Mr Ahern, who insisted there was no "ulterior motive" behind the failure to tell the Progressive Democrats.
Yesterday, the Tánaiste, Ms Harney, who has campaigned on the basis that the Progressive Democrats can be a "watchdog" on Fianna Fáil in government, sought to play down the significance of the Burke appointment.
"This individual is already a member of the Port Authority. So I don't know what people are saying. Are they saying he is not suitable to be chair?
"I can't put my hand on my heart and tell you that if we had been consulted that we would have said 'no' because I don't know what reasons we could have given," she said.
"To be honest with you, this is not the biggest issue around. The biggest issue for me is to ensure that we have a coalition government."
Mr Ahern said that normally the government parties would be in regular contact about appointments to the most influential, and most sought-after, State boards, such as the IDA and Aer Lingus, but about "40 or 50" appointments were being made to a variety of port authorities on this occasion,
Mr Ahern said. "I have to say that I did not go into great detail, or discussion, or knowledge on it."
The issue was left to the Minister for the Marine, Mr Fahey to handle, he said.