Cardinal Seán Brady has said the provisions proposed in the Heads of the Protection of Life in Pregnancy Bill, if passed, would permit the direct intentional killing of an innocent life.
He said that is morally unacceptable.
Speaking on RTÉ's Six One News, Cardinal Brady said the draft legislation deprives the most fundamental right of all - the right to life of the unborn child.
He said that efforts to protect the life of a mother were commended but questioned who speaks for the life of the child.
In relation to the court judgment on the X Case, Cardinal Brady said he understood that the judgement, while it requires the production of guidelines to provide clarity and certainty, it does not demand that there should be legislation for abortion and therefore the church does not see that this is necessary.
He said the bishops do not believe that the taking of an innocent life can ever be a remedy for suicidal ideation and what was needed for women in such a tragic situation was help, support, love, affection, care and that must come from outside.
Cardinal Brady said the scandal involving clerical child sex abuse did not exempt the bishops from the duty of proclaiming the good news of the gift of life.
Bishops issue statement on proposed legislation
Earlier today, the Catholic Bishops of Ireland said the Protection of Life in Pregnancy Bill represents a dramatic and morally unacceptable change to Irish law.
In a statement, they said the bill was unnecessary to ensure that women receive "the life-saving treatment they need during pregnancy".
They said: "The deliberate decision to deprive an innocent human being of life is always morally wrong.
"The Bill also appears to impose a duty on Catholic hospitals to provide abortions.
"This would be totally unacceptable and has serious implications for the existing legal and Constitutional arrangements that respect the legitimate autonomy and religious ethos of faith-based institutions.
"It would also pose serious difficulties for the conscientious beliefs of many citizens."
Reacting to the bishops' statement, Tánaiste Eamon Gilmore said while they are entitled to their view, Ireland is a democratic country and laws are made by those elected by the people.
He said for 21 years legislators failed to legislate in circumstances where a pregnant woman's life was at risk and that is now being addressed.
Professor of Psychiatry at Trinity College Dublin Veronica O'Keane has said psychiatrists are legitimately deemed best placed to assess suicide risk and if there was a mental illness in a woman it would be their role to treat that illness.
Speaking on RTÉ's Today with Pat Kenny, Prof O'Keane said if there was the presence of mental illness it sometimes would make a doctor less likely to recommend an abortion.
She said situations are different, and she thought it was much easier to make a decision in the absence of mental illness.
"I think this legislation is primarily for women who are suicidal because they have an unwanted pregnancy and that is the only way of resolving their suicidal problems - is to have a termination," she said.
Responding after the programme, Psychiatrist Prof Patricia Casey said that the legislation will allow for abortion in the case of women without mental illness, who simply do not wish to give birth to an unwanted baby.
Prof O'Keane also described as "an absolute farce" a survey by a "pro-life" group that claimed 120 psychiatrists who responded did not agree with proposed legislation to legislate for the X Case based on the suicide provision.
Prof Keane said it was a survey conducted by a statedly-biased group and it was done without the permission of the College of Psychiatry Ireland.
She said that those conducting the survey had not gone through the college's procedures and the survey would not have passed through the college's guidelines.
She said the survey did not represent psychiatrists.
Describing the survey as it stood as "incomprehensible, and garbled", she said it did not make any sense.
Prof Casey threatened to leave the studio if she could not respond.
Prof Casey said that the reason they did not do the survey through the college was because they could not get the names of the college membership, in relation to a previous study.
So, she said, when this study was happening she said that "they could not get the numbers from them".
In a statement following the programme, Prof Casey said: "This was not a College of Psychiatry survey, nor did it purport to be. It was a letter that was sent, asking consultant psychiatry colleagues if they agreed with a particular statement, relating to the involvement of psychiatrists in relation to the current abortion proposals.
"The issue of obtaining permission from the college does not apply. We received a 42% response rate, and it cannot be reasonably argued, by Prof O'Keane, that it was incomprehensive. The overwhelming majority agreed with the statement.
"The question of peer review does not arise."
FF seeks 'consensus' on abortion legislation
Elsewhere, Fianna Fáil health spokesperson Billy Kelleher said the leadership of the party wants to reach a consensus on the Protection of Life in Pregnancy Bill.
However, Mr Kelleher said that he was not sure that would be possible.
Speaking on RTÉ's Morning Ireland, he said that the party does not want to be divisive.
He said Fianna Fáil is seeking to be constructive in its contribution to this debate.
Mr Kelleher said that there were strong views on both sides and there were concerns about technical issues in the bill, as well as fundamental principles, such as intervention on mental health grounds.
However, Mr Kelleher said that he did not think the term "split" accurately described the situation in the party.
The Cork TD said that he personally would recommend acceptance of the bill.
However, he remains mindful of divergent views both within his party and more broadly.
Mr Kelleher will be attending the Oireachtas Committee hearings on the bill and will be putting concerns raised by the party to it.
The party met for more than four hours yesterday to discuss the legislation.
His colleague, Willie O'Dea, said the Fianna Fáil party will find it very difficult to achieve a consensus approach.
The witness list for the Oireachtas committee hearings is expected to be finalised on Tuesday.
It is expected to hold hearings over three days - 17 May, 20 May and 21 May - and will hear from legal and medical experts.
As well as hearing from expert witnesses, the committee will also take written submissions from interested parties and members of the public.
Details of how to submit written evidence will be on the committee's website.