Assembly members yesterday voted against a Sinn Fein proposal to legalise same-sex marriage, by 53 votes to 42.
Patrick Corrigan, Northern Ireland Programme Director of Amnesty International, warned that the political inaction is "leaving tough decisions to judges, who often receive the flak from those same politicians" who blocked reform.
Under a series of changes to the law in other parts of the UK, legislation governing same-sex marriage, adoption and gay men donating blood has been rewritten or relaxed.
But those changes continue to be blocked by politicians in Northern Ireland.
Stormont has also been criticised for excluding Northern Ireland from sweeping reforms aimed at strengthening freedom of speech.
The Defamation Bill – which brings Britain's Victorian libel laws into the 21st century – was passed in both houses of Parliament last week. But the Act has been blocked here – prompting warnings that Northern Ireland could become a hotspot for so-called libel tourism.
Britain's libel laws are seen as among the most restrictive in the world, with British courts being used by foreigners to sue international publications under the UK's punitive regime.
Jo Glanville – a civil liberties campaigner and Director of liberal reform campaign group, English Pen – said that Stormont's unexpected move gave "libel bullies" a corner of the UK in which to operate.
"Stormont has blocked the (Defamation) Act from becoming law in Northern Ireland, which means that libel bullies will still have a small corner of the UK until the Assembly sees sense," she said.
The Bill's architect, Liberal Democrat peer Lord Lester, has already warned that Stormont's failure to extend the reforms to Northern Ireland could mean Belfast becomes the UK's new libel capital.
The overall move against reform is particularly damaging for Northern Ireland society, Patrick Corrigan told the Belfast Telegraph yesterday.
"I think there is that sense that parliaments and assemblies in other parts of the UK, and across the border in the Republic of Ireland, are voting to address past inequalities and discrimination and to update law. And on every count, Northern Ireland appears to be left behind," he said.
"In terms of brass tacks, what that means is that certain sections of Northern Ireland's community are facing inequalities not faced by people in other parts of these islands, and feeling that their politicians are not willing to show leadership."
Northern Ireland is the only part of the UK where a ban on gay and unmarried couples adopting children in remains. A High Court judge recently ruled that the ban is discriminatory.
Health Minister Edwin Poots has also been ordered to release advice from the Attorney General which he used to justify a lifetime ban on gay men giving blood. Rules banning gay men from giving blood were relaxed across the rest of the UK in November 2011.
Last month, human rights campaigners – including Amnesty International – vowed to fight a ban on same-sex couples marrying in Northern Ireland. The UK's first gay civil partnership ceremony was held in Belfast.
"The international trend is to eradicate these past inequalities," Patrick Corrigan added.
"And Northern Ireland risks being badly left behind."