The government is expected to hold a ceremony in the western Niger town of Tillaberi, on the edge of the Sahara, to explain the law to people who have spent their whole lives as the property of their masters.
The chief of the In Ates region will free all slaves in the area under his control, where entrenched slavery means 95 % of the population are owned and controlled by the other 5%.
The announcement marks the first major push by the government to publicise an anti-slavery law passed in May 2004. At least 43,000 people live as part of an established slave class in across Niger, according to a study carried out in 2003 by Niger anti-slavery organisation Timidria in collaboration with Anti-Slavery International.
Slaves in Niger are generally born into an established slave class that works without pay for masters who control every aspect of their lives. Babies are taken from their mothers to prevent bonds being formed in families, and sexual assault and rape are widespread. Slaves are given as gifts or inherited among the slave-owning class.
Those held in bondage have little access to radio and are largely illiterate, so few realise that the law says they can leave their masters if they wish. For many, a lack of economic prospects may mean life does not change very much even once they have been officially freed.
"This is the first step towards their full emancipation," said Romana Cacchioli of Anti-Slavery International. "Slaves are considered animals and have been treated as such."
Ms Cacchioli said that the full implications of freedom would probably not be apparent to people who have lived all their lives in bondage, and that a major programme of civil education and humanitarian assistance would be necessary to engage the huge slave class as full and equal citizens.
"We need to explain to them what being a citizen means. Masters no longer have control over their lives, masters cannot make them work for no pay, masters cannot control who they marry or take their children away," she said.
Niger is one of the world’s poorest countries, with an average life expectancy of just 42 years and over 60% of the population living in poverty. Freed slaves will face a stark lack of resources, as masters still own the animals, equipment and agricultural resources on which the largely agrarian economy depends.
The Niger government does not have the resources to back up the criminalisation of slavery, Ms Cacchioli said, and she hoped that the French and British governments, along with international aid agencies, would provide much-needed assistance to set up schools, provide access to clean water, and provide livestock and seeds to freed slaves.
A spokesman for the Foreign Office said the British government had no involvement in Niger’s attempts to free its slave population, though it had engaged in talks with Niger on debt relief.
Despite the challenges they face, Ms Cacchioli said the reaction from freed slaves she had spoken to was overwhelmingly hopeful.
The younger generation would probably take greater immediate advantage of the situation, and there was a lot of anger among young male slaves in particular, she said, adding that the courts in Niger were already hearing cases of slaves fighting for freedom from masters who refused to acknowledge the new law.
"We would rather work through mediation, but if there are masters who refuse to release slaves then we will not hesitate to use the courts," she said.