Pakistan's Supreme Court Wednesday overturned the conviction of Asia Bibi, a Christian mother facing execution for blasphemy, in a landmark case which has incited deadly violence and reached as far as the Vatican.

‘The appeal is allowed. She has been acquitted. The judgement of high court as well as trial court is reversed. Her conviction is set aside,’ said Pakistan's Chief Justice Saqib Nisar in the ruling.

Blasphemy is an incendiary charge in deeply conservative Pakistan, where even unproven allegations against religion can provoke a violent and bloody death at the hands of vigilantes.

Bibi was set to be released immediately according to the court, although there was no word if any security arrangements were being made for her protection.

Her legal team celebrated the court's decision amid beefed-up security in Islamabad after religious hardliners had vowed to protest any acquittal of the case.

‘The verdict has shown that the poor, the minorities and the lowest segments of society can get justice in this country despite its shortcomings,’ Bibi's lawyer Saif-ul-Mulook told AFP.

‘This is the biggest and happiest day of my life.’

Her case drew the attention of international rights groups and swiftly became the most high-profile in the country.

Pope Benedict XVI called for her release in 2010, while in 2015 her daughter met his successor and the current head of the Catholic Church, Pope Francis.

The allegations against Bibi date back to 2009, when she was working in a field and was asked to fetch water. Women she was labouring with allegedly objected, saying that as a non-Muslim she was unfit to touch the water bowl.

The women went to a local cleric and accused Bibi of blasphemy against the Prophet, a charge punishable by death under colonial-era legislation.

- Landmark case -

During the appeal hearing on October 8, a three-member panel of Supreme Court justices appeared to question the case against her, with Justice Asif Saeed Khan Khosa, considered Pakistan's top expert in criminal law, listing flaws in the proceedings.

‘I don't see any derogatory remarks as per the FIR,’ added Chief Justice Saqib Nisar, referring to the initial complaint filed in the case.

Approximately 40 people are believed to be on death row or serving a life sentence in Pakistan for blasphemy, according to a 2018 report by the United States Commission on International Religious Freedom.

Leading rights groups have long criticised the legislation, saying it is routinely abused to justify censorship, persecution, and even murder of minorities.

In recent years, it has also been weaponised to smear dissenters and politicians.

Mere calls to reform the law have provoked violence, most notably the assassination of Salmaan Taseer, the governor of Pakistan's most populous province Punjab, by his own bodyguard in broad daylight in Islamabad in 2011.

Taseer had also called for Bibi's release. His assassin, Mumtaz Qadri, was executed in 2016 and has been feted as a hero by hardliners, with a shrine to him built just outside the capital.

Taseer's son Shahbaz tweeted ‘Pakistan Zindabad’, meaning ‘Long live Pakistan’, following the ruling.

Politicians including new prime minister Imran Khan invoked blasphemy during a general election this summer, vowing to defend the laws.

Analysts have warned the tactic could deepen sectarian fractures and potentially spill into violence.