A 24-year-old woman who spent her life as a slave has taken the Niger government to court, claiming it failed her by ignoring its own laws. Peter Beaumont and Alexander Carnwath report

In one of the most extraordinary episodes in African legal history, a panel of judges from Senegal, Mali and Togo will tomorrow issue a verdict expected to give fresh hope to more than 40,000 people being held as slaves in rural Niger and across the region.

The landmark case of Hadijatou Mani, a courageous young woman of 24, will be heard in a packed court in Niger's capital, Niamey, which will decide whether Niger's government has failed to protect Ms Mani and tens of thousands like her who have been enslaved, despite the practice being outlawed five years ago.

If she wins her case, which is being heard by the justice arm of the Economic Community of West African States (Ecowas), she is likely to be awarded compensation of up to £40,000, in a humiliating reversal for the authorities she blames for her lost youth.

Ms Mani was sold into slavery at the age of 12 and repeatedly raped by her master. Her appalling story is familiar in a country where the ownership of slaves, many from a hereditary slave caste, has been commonplace, particularly in remote rural areas.

Speaking before the judgment, Ms Mani said: 'It was very difficult to challenge my former master and to speak out when people see you as nothing more than a slave. But I knew that this was the only way to protect my child from suffering the same fate. Nobody deserves to be enslaved.

'We are all equal and deserve to be treated the same as anyone else. I hope that all those who are in slavery today can find their freedom. No woman should suffer the way I did.'

Helen Duffy, a lawyer who has represented Ms Mani, said: 'I'm really optimistic. It is such a clear case. She has suffered so much. It is just the clearest violation.'

The life of a sadaka - sexual slave - has been described in detail by Ms Mani in the court, in front of some of the country's most senior political figures. Speaking nervously at first, she told the court how she had been born a slave, been sold and transferred as a child against her mother's wishes to a man named El Hadj Souleymane Naroua. She testified that she had been raped at 13 and constantly forced to have sex with her 63-year-old master, who owned seven other slaves.

Beatings were frequent and she and other slaves were forced to work unpaid and gruelling hours for Naroua and his four legitimate wives. When she tried to escape, she was punished.

In 2005, two years after Niger enacted a law forbidding slavery, she was presented with a 'liberation certificate'. This proved to be worthless, as she was immediately forced into a 'wahiya marriage', with the status of a concubine. When she fled and married another man, her master had her arrested and charged with bigamy. She was subsequently imprisoned for two months on remand. It is believed that if tomorrow's verdict goes in her favour, the bigamy charges will be dropped.

'You could see her grow in stature through her testimony,' said Duffy. 'When she was done we left the courtroom and, for the first time, I saw her smile; an enormous, satisfied smile. She was justifiably very proud of herself.'

The issue has become a deeply embarrassing one for the government of Niger. Despite introducing the anti-slavery legislation, it has failed to act on evidence of its continuing and widespread existence in rural areas.

One Nigerien official told the UN committee on the Elimination of Discrimination Against Women in 2007 that he could prove that 'slavery does not exist in Niger'.

As well as being banned under Nigerien law, slavery is outlawed under many of the international agreements Niger has signed up to, including the UN Slavery Convention of 1926 and the African Charter on Human and People's Rights.

But international conventions and national laws count for little compared to the centuries old 'customary law' that holds sway in rural villages and towns. According to Anti-Slavery International, Niger's courts have frequently proved reluctant to enforce law over custom. In one case in 2006, both the sentence and fine against one slave owner, Seidimou Hiya, were massively reduced.

The case of a 15-year-old girl who sought help from Timidria, a Nigerien anti-slavery group, after fleeing her slave master, was thrown out after the local prosecutor ruled that she was a 'disobedient girl'.

Ms Mani's case against the government rests on witness testimony, including that relating to her sale to Naroua. The government's witnesses, tribal chiefs, have claimed not to understand the terms of enslavement, then changed their evidence twice.

'We are hoping for a strong message on this,' said Romana Cacchioli, Africa programme officer of Anti-Slavery International, which worked with Timidria to bring the case. 'It would send out a clear message that the longstanding prohibition of slavery must be enforced.

'Although it's all well and good that states ratify human rights conventions, we need them to ensure effective implementation. We hope the court will recommend the state trains its judicial staff and raises the issue of slavery through a national publicity campaign. It is not the state of Niger which is perpetrating slavery, it is individuals, but the state has a responsibility.

'Hadijatou is really impressive. She comes across as very unassuming. She knows she has been wronged. She was in court with her baby strapped on her back. She says she does not want the same thing that happened to her to happen to her daughter. Her vision is in terms of others.'

Campaigners hope a favourable ruling may herald a major cultural shift on the issue of descent-based slavery throughout the Sahel region. The court's judgment will be binding in Niger and will be applicable in other countries in the Ecowas community where descent-based slavery exists, including Mali.