It is estimated there are only 400 ploughshare tortoises left in the wild in Madagascar.
They are sought after as exotic pets and because of their high domed shells.
The Jersey vet flew to Singapore Zoo and engraved identifying codes on to tortoise shells to reduce their value on the black market.
At the Tattoo the Tortoise event, Durrell's Malagasy veterinary officer Tsanta Fiderana was responsible for engraving the shells of the rare reptiles.
Mark Brayshaw, head of animal collection at Durrell, said: "We are facing a huge challenge to prevent the ploughshare tortoise from being lost forever in the wild due to smuggling for the pet trade.
"With continued commitment from the local communities, the Malagasy Government and the international conservation community we can protect the tortoise's habitat and halt the illegal trafficking."
Ploughshare tortoises are being bred at Singapore Zoo to establish an "assurance colony".
This would ensure their survival in the event of the wild population being eradicated.
Most of the illegally exported tortoises are sold in markets in the nearby south-east Asian nations of Indonesia, Malaysia and Thailand.
Wildlife Reserves Singapore, TRAFFIC and the Turtle Conservancy were also involved in the tattooing project.
An expert from Jersey's Durrell Wildlife Park has been helping protect critically endangered tortoises from smugglers by marking their shells.