Fianna Fáil leader Micheal Martin says he believes the 8th amendment should be removed from the Constitution.
He was speaking during the second day of debates in the Dáil over the issue of abortion.
Mr Martin said: "Because it requires that pregnant women and doctors are faced with criminal sanctions.
And because it prevents us from responding in a humane way in order to help women in the most traumatic situations.
"For these reasons, and following a long period of reflection and assessment of evidence before the Oireachtas Committee, I believe that we should remove the 8th amendment from Bunreacht na hÉireann and I will vote accordingly."
More TDs and Senators are give their opinions on the recommendation of allowing abortion without restriction for up to 12 weeks.
Labour TD Jan O'Sullivan quoted some of the evidence the committee heard.
She read a statement given by a couple who traveled to the UK for an abortion because of a fatal foetal abnormality.
"If we have our car we can bring our baby home on the boat - this journey involves us having to go to a supermarket to buy freezer packs, and then we have to stop at regular intervals to open the coffin and change them so that we can keep our baby cold.
"We also have to leave our baby in a coffin in our car, covered by a blanket or in the boot, while we cross the Irish Sea".
Fine Gael TD Kate O'Connell accused the church and State of historical collusion on issues like contraception and abortion.
She said when Ireland has been at its most Catholic, its been its least Christian.
"The church and the State were colluding to subjugate and inter fallen women in Catholic-run and State-subsidised prisons, punishing them for the sin and sex and the flaw of being female.
"Irish women were quite literally enslaved in an act of church and State collusion that could be honestly characterised as nothing other than sexual apartheid."