Tánaiste Eamon Gilmore hailed the President’s move as marking a milestone in Irish legal history and offering long-delayed protection to women.
However, the Pro-Life Campaign said it would fight to have the law repealed.
Mr Higgins acted quickly after convening the Council of State as he had until midnight tonight to decide.
If Mr Higgins had sent it to the Supreme Court and judges had upheld its constitutionality, the Protection of Life During Pregnancy Bill would not have been able to be challenged on those grounds again.
Now signed into law, the provisions for abortion in tightly designated circumstances where there is serious threat to the life of the mother, is open to being challenged in the courts.
Mr Gilmore said enactment of the bill was a long-awaited reform.
“The core purpose of this legislation is about saving women’s lives. It is about providing for a very basic human right. The tragic death of Savita Halappanavar highlighted the legal uncertainty faced by doctors in dealing with medical emergencies where the life of a woman is at risk,” Mr Gilmore said.
However, the Pro-Life Campaign’s Caroline Simons warned Fine Gael would pay a price at the next general election for legislating for the X-Case.
“The new law is life-ending not life-saving. The Government brought forward this law in the full knowledge that abortion is not a treatment for suicidal feelings and ignored all the peer-reviewed evidence showing that abortion has adverse mental health consequences for women.
“The Pro-Life Campaign will now devote its energies to the repeal of this unjust law. We will give very careful consideration in the coming weeks on the best way to bring this about,” she said.
A legal challenge to the Act in the High Court and then the Supreme Court could prove very expensive, but observers expect a case to be launched in the near future.
The Council of State, comprising present and former office holders, legal experts and the president’s appointees, met for more than three hours on Monday to discuss the legislation and whether it should be referred to the Supreme Court. Mr Higgins was not obliged to take the advice as sending Bills to the Supreme Court is one of the few powers the president exercises under the constitution.