Ms Simons told the crowd that claims by the Government that abortion was needed to treat threatened suicide in pregnancy had been “completely demolished at last week’s Oireachtas hearings on abortion”.

She said: “The psychiatrists who addressed the hearings were unanimous that abortion is not a treatment for suicidal ideation.

“There is no evidence whatever that suggests that abortion reduces the mental health risks of unwanted or mistimed pregnancy. But there is evidence that abortion increases the risk of future mental health problems for a significant number of women,” she said.

Speaking at the vigil, Tyrone football manager Mickey Harte said that “Quite frankly I am most concerned that this Government proposes to legislate for abortion”.

“Ireland is almost unique in the western world in looking out for, and fully protecting, two patients during a pregnancy – a mother and her unborn child,” he said.

“We are here to oppose the unjust targeting of even one unborn child’s life in circumstances that have nothing to do with genuine life-saving medical interventions,” Mr Harte said to rapturous applause from people who had travelled from all over Ireland.

One of the highlights of the event, which was held on Dublin’s Merrion Square, was a live phone call to Taoiseach Enda Kenny where everyone chanted ‘keep your promise’ – a reference to Mr Kenny’s pre-election pledge not to legalise abortion.

The massive pro-life event went quiet as Dr Eoghan de Faoite of Youth Defence called an Taoiseach’s constituency office, and Mr Kenny’s voice could be heard asking the caller to leave a message.

“Hello an Taoiseach, this is the Vigil for Life, and I have 30,000 people here to give you a reminder of the pro-life promise you made in 2011,” said Dr de Faoite.

“The vigil has been a tremendously powerful and historic event, and the voice of the majority has been heard for the protection of both mother and baby,” said Dr de Faoite.