Vincent and Yasmina Bardet were sentenced to five months and fined pounds 10,000 each for "using a person's labour without payment". They employed Henriette, a Togolese woman, for three years in their Paris apartment without giving herwages or time off.
Mr Bardet is a publisher and the son of the founder of the French publishing house Seuil. Foreigners and immigrants have been convicted for exploiting immigrants in this way. But this is the first conviction of French citizens for using an illegal immigrant as unpaid domestic labour.
A neighbour of the Bardets had contacted a pressure group called the Committee against Modern Slavery, which informed police. Mr and Mrs Bardet told a court last month that they regarded Henriette - 16 when she joined them - as an "au pair" and a happy member of the family.
They said they had given her a lump sum and they had put money into a "kitty" for her, to make sure she was not "cheated" and "made something of her life".
No evidence was produced to substantiate the claims, which were rejected by the court in a delayed judgment. Henriette, now 21, said she was expected to look after the couple's three children, to do the washing and the housework.
She was not allowed to go out without permission and then usually only to collect the children from school. She slept on a mat in the children's room. She did not receive wages. At one point, she ran away to her uncle's home in another part of France but he brought her back to the Bardets, on condition that they sought residence and work permits for her.
Mr Bardet, who describes himself as a humanist, told the court he had tried to fulfil this promise but gave up because it was "an uphill struggle". The public prosecutor, Nicolas Blot, told the court: "This case is no different from clandestine sweat-shops. We are not in the 17th century in a country far away, but at the dawn of the third millennium in the country which invented human rights."
As part of an agreement with the state prosecution service, Henriette is shortly to be given a work permit. She has been learning to read and write and hopes to train to become an auxiliary nurse.