Four men – three Irish and one English – said to be members of the Rathkeale Rovers gang were given prison terms, though two were spared jail as the sentences were suspended.
The court also imposed a total of €316,000 (£270,000) in fines.
Three of the men were not present at the special court in Rennes in west France and are the subject of international arrest warrants.
Charlotte Nithart, president of the Robin des Bois (Robin Hood) environmental group, welcomed the judgment she said was “educational and dissuasive … for all those who engage in wildlife trafficking and speculate on species threatened with extinction”.
“Before trafficking, there is poaching which causes social and environmental devastation,” she said after Wednesday’s verdict.
French prosecutors began investigating after police stopped a BMW car in a random motorway traffic inspection in September 2015 and found four uncertified elephant tusks and €32,800 in cash.
The occupants of the car, some of whom claimed they were antique dealers, were later found to be part of an international network of rhino horn and ivory traffickers including several of Chinese and Vietnamese origin.
Police said the Irish and English suspects were members of the Rathkeale Rovers, a criminal clan named after a town outside Limerick in southern Ireland. Rooted in the Travelling community, gang members have been linked to a bewildering range of scams across Europe, the Americas, Africa and Australia.
Detectives discovered the smugglers had two workshops in France to transform ivory and rhino horn into powder or flakes and other objects that were then exported to Vietnam and China to be used in traditional medicine.
One large horn weighing nearly 15kg was seized during the investigation. Robin des Bois said it would have been worth around €13m in exported products once processed.
Robin des Bois alleged that auction houses in Cannes, Toulouse and Le Puy had facilitated the export of tusks to Vietnam and China.
The Rathkeale Rovers were the target of a joint investigation by European police in 2010 that led to 31 people being arrested, including for the theft of rhino horns, the Europol police agency says on its website.
The gang has traded in illicit antiques, cigarettes, electrical goods, vintage cars and fake coronavirus test certificates.
It has tarmacking scams that con customers and contractors, earning nicknames in several languages: “asfaltaris Irlandese” in Italy, “teerkolonne” in Germany and “les faux bitumeurs” in France. The tarmackers have also reportedly operated in South America, Mexico, the US and South Africa.
Europol warned in February that members of the Rathkeale Rovers were using a mobile phone app to falsify coronavirus test results which were then sold to travellers.
In 2017 a federal court in Miami sentenced Michael Hegarty, regarded as a senior member of the gang, to 18 months in prison for smuggling a libation cup – a drinking vessel carved from rhino horn – from the US to England.