The Republic will make history tomorrow.

That’s if the polls are correct and a majority opt for Yes in the marriage equality referendum. If that happens, Ireland will become the first country in the world to legalise same-sex marriage by popular vote.

An IPSOS/Irish Times survey, taken last week, shows that, excluding undecided voters, 70% of people intend to vote Yes, while 30% for No.

However, Yes campaigners are warning against complacency, advising the outcome is likely to come down to which side can ‘get the vote out’. Older voters, arguably more likely to oppose the change, constitute the demographic which is traditionally most likely to vote. But there are reports of a surge of late voter registration among first-time and younger voters, energised by the prospect of shaping Ireland as a forward-looking place to live.

While all the main political parties are, with varying degrees of enthusiasm, backing a Yes vote, it is the civil society Yes Equality initiative which has led the campaign.

Amnesty International has been prominent among the campaign groups pressing for a Yes vote, making clear that the referendum is about equality and the fundamental human right not to suffer discrimination on the basis of sexual orientation, while dissecting some of the red herrings promoted by the No campaign.

On the face of it, the level of popular support for same-sex marriage is extraordinary, when one considers that the Republic only decriminalised homosexuality in 1993, five years after a finding by the European Court in Strasbourg that Ireland’s anti-gay laws were in breach of the European Convention of Human Rights.

But the Republic has been changing rapidly over recent decades. In particular, the country has become increasingly secular, with the influence of the Catholic Church – moral authority tarnished by repeated scandal – in decline. While the bishops have published the expected pastoral letters arguing against change, it feels like there is none of the conviction of days of old, when they could expect church goers to follow meekly. Numerous members of the clergy have gone public with their intention to vote Yes. Prominent Catholic layperson and former President, Mary McAleese has revealed that she contemplated leaving the Church over their attitude towards gay people, as she related how her son Justin experienced homophobic bullying while growing up in unequal Ireland.

If the opinion polls translate into a Yes vote tomorrow, the Republic will join England, Scotland and Wales in legislating for same-sex marriage.

Of course, that means that Northern Ireland will be left as the only part of these islands where gay couples will continue to be denied the right to get married. Our politicians have now voted on four occasions to reject same-sex marriage in the Assembly. Indeed, the DUP has vowed to use a petition of concern to veto any same-sex marriage Bill, even if it has majority support among MLAs, which appears certain if SDLP and Alliance MLAs did not go ‘missing in action’ during crucial votes.

Given this political failure, it seems that recognition of same-sex marriages will only happen in Northern Ireland via the courts, a move which Amnesty backs.

It’s clear the parties are out of step with the people. The 2013 NI Life and Times Survey showed 59% to 29% support for same-sex marriage in the north, even before the measure was introduced in the rest of the UK. With same-sex marriages increasingly commonplace elsewhere, those figures would likely be even higher now.

A resounding yes vote in the Republic will echo around the world – of how a once socially conservative country can choose to cherish, in the words of the 1916 proclamation, ‘all the children of the nation equally’. In a world where prejudice against and persecution of LGBTI people is still commonplace, the power of that message should not be underestimated.

For now, though, the marriage equality campaign is focused on the south, and human rights campaigners in Northern Ireland are calling for a strong Yes vote, knowing that success there will build unstoppable momentum north of the border.

The right to equal civil marriage for gay people will come to Northern Ireland. It’s now a matter of when and how, not if.

A version of this article appears in today’s Irish News.