By Q Radio News
Pro-choice and anti-abortion activists gathered outside Parliament Buildings on Monday morning ahead of the Assembly sitting.
Sarah Ewart, who has become a vocal advocate for reform since having to travel to England for an abortion after receiving a diagnosis of fatal foetal abnormality, welcomed the decriminalisation.
"This law change will not fix what I had to go through but it will make it hopefully better for those who follow after me," she said.
Grainne Teggart from Amnesty International said the law change would pave the way for a more "compassionate" system.
"From midnight tonight history will be made, these oppressive laws that have policed our bodies and our healthcare will be brought to an end," she said.
"Finally our rights and our healthcare are being brought into the 21st century."
Anti-abortion activists held up placards stating that the decriminalisation was not in their name.
They also prayed beneath the landmark statue of Sir Edward Carson.
Activist Clive Johnston, from Strabane, warned of the consequences of decriminalisation.
"In today's world the most dangerous place to be is actually in the womb of a woman," he said.
"The Government is culpable in actually taking part in what amounts to the killing of babies in the womb."
Director of Precious Life, Bernadette Smyth, says abortion is ‘not in the name’ of Northern Irish people: pic.twitter.com/EZiFCDzMAG— Q Radio News (@qnewsdesk) October 21, 2019
The start of the Assembly sitting has been delayed until 1pm.
It is understood the postponement relates to legal issues.
Northern Ireland's Attorney General John Larkin was seen in Parliament Buildings during the morning.
At the start of proceedings, there was a bid by anti-abortion MLAs to fast-track a piece of private members' legislation through in a single day to thwart the abortion reform.
DUP Paul Givan MLA urged the suspension of standing orders to enable the bill to be considered.
However, current speaker Robin Newton said a new speaker would need to be in place before the Assembly could turn to such a legislative bid.
Mr Newton said a further sitting of the Assembly would be required to consider the bill and highlighted that the suspension of standing orders required cross-community support.
He said it was "not good practice" to take a piece of legislation through in one day.
"The Assembly cannot do any business until a speaker and deputy speakers are elected," he said.
Mr Givan insisted that advice from Attorney General Mr Larkin indicated that standing orders could be suspended to allow the legislation to be considered.
Same-sex couples and marriage equality campaigners have held an early celebration at the Merchant Hotel in Belfast ahead of a change to the law in Northern Ireland.
From midnight, if no Northern Ireland Executive has been re-established, Westminster is legally obliged to make marriage available to same-sex couples in the region, following legislation passed during the summer.
More than a dozen same-sex couples along with campaigners enjoyed wedding cake following a buffet reception surrounded by flowers and balloons before cheering on the steps of the hotel, many holding signs which read "equal".
The event was organised by the Love Equality campaign, which is led by the Rainbow Project, Amnesty International, Irish Congress of Trade Unions, Cara-Friend, NUS-USI and Here NI.
Patrick Corrigan, Northern Ireland director of Amnesty International, said the moment comes after years of campaigning.
"Today, we celebrate success, secured not because of the presence of Stormont, but because of its absence," he said.
"Despite overwhelming popular support for change, sadly the Executive and Assembly repeatedly failed to deliver marriage equality and abortion law reform.
"When Stormont collapsed, we took our campaigns to Westminster.
"This is an incredible moment for so many people, especially for same-sex couples who will now be treated as equal citizens in their own country."
DUP leader Arlene Foster said it was a "shameful day".
"This is not a day of celebration for the unborn," she said.
Ms Foster said decriminalisation at midnight would not mark the end of efforts to prevent the introduction of abortion services in the region.
She said her party would explore "every possible legal option" open to it.
Ms Foster said the law change would see Northern Ireland adopt the most liberal abortion regime anywhere in Europe.
The sitting of the Assembly ended when it became clear a speaker could not be elected.