32-year-old Hind Ahmas and Najate Naït Ali, who is 36, were ordered to pay fines of 120 euros and 80 euros respectively.
The two women arrived late and were not able to enter court to hear the judge's pronouncement.
At the hearing in May, one of them turned up outside the court, but was not allowed to enter because she refused to remove her full veil and reveal her face.
Yann Gré, who is the lawyer for the two women, declared that they will appeal against the ruling and are ready to take the case before the European Court of Human Rights.
Some women have already been given verbal warnings by police officers on the street, but this is the first time that such a case has reached court.
Several women wearing the niqab turned up outside the courthouse to support the women.
Among them was Kenza Drider, who announced that she intended to stand as a candidate in France's next presidential elections in May 2012.
The law was introduced in 2010, and came into force in April this year, after a six-month adaptation period.
Under its terms, it is illegal for anyone to cover their face in a public place.
The ban includes veils and balaclavas, with exceptions made for crash helmets, carnivals and other special cases.
If someone refuses to uncover their face when stopped by a police officer, the person is liable to a fine of up to 150 euros and/or a citizenship course.
According to the association "Hands off the Constitution", half of the estimated 2,000 women who wore the full face-covering Islamic veil before the introduction of the law, have now abandoned it, at least in public.
The law was first proposed by a Communist MP in France.
A commission of enquiry took evidence from a variety of representatives, including muslim groups and women's groups, before recommending a law.
The law was then introduced by a member of Nicolas Sarkozy's ruling conservative UMP party.