The ban on gay marriage makes Northern Ireland stand out as a backward-looking blot on the map, a High Court judge has been told.
Two couples, Gráinne Close and Shannon Sickles and Chris and Henry Flanagan-Kanem, have been granted permission to judicially review the Stormont Assembly's repeated refusal to legislate for same sex marriage.
They were, respectively, the first and second couples in the UK to enter into a civil partnership after Northern Ireland became the first part of the UK to make that option available in December 2005.
Following the Yes vote in May's referendum on marriage equality here, Northern Ireland is the only part of the UK or Ireland where civil marriage is denied to gay couples.
Barrister David McMillen QC told Belfast High Court: "Northern Ireland stands as a blot on the map; a backward looking, divisive and divided society."
The prominent case is being heard before Mr Justice O'Hara at Belfast High Court.
The issue was debated at Stormont for a fifth time last month.
Although the majority of MLAs voted in favour of introducing gay marriage, the proposal fell because unionists who oppose the move deployed a controversial voting mechanism to effectively veto it.
The court heard that the current bar amounted to State discrimination of an already marginalised section of society.
Mr McMillen added: "The love and life long commitment of these four applicants is the same as any other couple.
"It is demeaning and offensive that the union had been relegated to a second class status - civil partnership."
Both couples have been together since 2002, it was revealed.
The male applicants, who were not in court, also have a young son.
Earlier this year about 20,000 campaigners staged a march through Belfast city centre demanding a change in the law.
Mr McMillen said: "If history, and in particular the history of Northern Ireland, tells us anything it is that discrimination of a being and private life is wrong. It keeps individuals apart from mainstream society and is corrosive to the very fabric of society."
Amnesty International, which is supporting the case, has described the case as "hugely significant".
Patrick Corrigan, Amnesty's Northern Ireland programme director, who was in court, said: "Following the repeated failure of the Northern Ireland Assembly to legislate for marriage equality, couples have been forced into the courtroom to demand equal treatment before the law.
"It is unacceptable that they have been obliged to sue the Government in order to have what the rest of society takes for granted - for the State to recognise their right to get married.
"With politicians having abdicated their responsibility to deliver equal treatment for same-sex couples, it is now over to the courts."
Meanwhile, in a separate case, also heard by Mr Justice O'Hara, two men who wed in England are seeking to have their marriage recognised in Northern Ireland.