Ireland’s vote in favour of same-sex marriage is a milestone in the global struggle for equality for gays and lesbians that has seen dramatic progress in many western countries while others slide backwards into further repression.

Homosexual activity remains illegal in almost 80 countries and in many, including Uganda, Nigeria, Russia and Egypt, the situation for gays and lesbians has worsened. Our Yes vote can serve as a beacon of hope not just for LGBT people on the brink of achieving equality but for those millions throughout the world who continue to face persecution, oppression and violence.

Marriage equality, which was a marginal, almost eccentric demand only two decades ago, is now a reality in 20 countries and in many sub-national regions, including 37 of the 50 states of the United States.

It is an entirely 21st century phenomenon, with the Netherlands becoming the first country in the world to allow gays to marry in 2001. It is also essentially a conservative one, which was initially resisted by radical gay rights campaigners who saw marriage as a repressive, patriarchal institution.

Tragic

The Aids crisis of the 1980s and early 1990s brought into sharp, tragic relief the consequences of the lack of legal recognition of gay partnerships as men were denied access to their dying partners in hospitals, were evicted from the homes they shared when loved ones died and had no inheritance rights. The initial response came in the form of domestic partnerships.

It was the gay conservative writer Andrew Sullivan who first put gay marriage on the agenda in the US in 1989 with a groundbreaking essay in the New Republic called "Here Comes the Groom". He argued that marriage would help to "humanise and traditionalise" gays by strengthening their relationships and providing emotional and economic security.

As in Ireland, what brought marriage equality into the mainstream in the US was the growing number of gays and lesbians coming out to friends and family. Greater visibility not only made gays and lesbians appear less exotic, it gave more straight people a stake in the debate as they backed equal rights for friends or family members.

Some 60 per cent of Americans now approve of same-sex marriage and the US supreme court will next month rule on Obergefell v Hodges, a set of four challenges to state bans on gay marriage. It is expected to rule that the bans are unconstitutional, a move that would effectively legalise same-sex marriage throughout the US.

Until 2010, when the states of Maine, Maryland, Minnesota and Washington approved same-sex marriage in referendums, the conventional wisdom in the US was that the issue could not win popular approval at the ballot box.

Progress

Most progress on the issue in the US has come through the courts, with referendums more often called to introduce bans on same-sex marriage than to lift them.

But the courts are not deaf to public opinion and the head of the European Court of Human Rights suggested in 2012 that the court could reconsider its view that same-sex marriage is not a human right if enough countries introduced it. The European Parliament last March passed a resolution recognising such a right, although just 10 European Union member-states, including Ireland, have marriage equality, with two more – Slovenia and Finland– set to join them within months.

Ireland has shown marriage equality can win popular support and Friday’s vote will encourage legislators and activists elsewhere in Europe to be bolder. The lessons of Ireland’s campaign will be useful elsewhere, just as the successful campaigns in the US in 2012 helped to guide Ireland’s campaigners.

Perhaps the central lesson is that it is less effective to simply demand rights than to persuade through personal testimony. It was stories such as those of Ursula Halligan, Pat Carey and Una Mullally that cut through the noise and appealed to the better nature of undecided voters. And straight allies such as Mary McAleese and Noel Whelan were eloquent in making the case that marriage was so important to them that they wanted to allow equal access to it.