He worked undercover in some of the world's most dangerous and difficult places, photographing and documenting ivory markets, talking to traffickers and calculating black market prices to guide global conservation policy makers.
In the last few years he travelled to China, Vietnam and Laos with collaborator Lucy Vigne, going into places few outsiders would dare to set foot, posing as ivory and rhino horn buyers.
In a Chinese-run casino in Laos, this odd couple would navigate gangsters, drug barons and traffickers of people, guns and wildlife to gather their data.
Their research, funded by Save the Elephants, revealed that Laos has become the fastest-growing ivory market in the world.
They had recently returned from an investigative trip to Myanmar and Mr Martin was writing up that data when he was killed.
Police are investigating the motive for his murder. He died from a knife wound to the neck at his house near Karen, outside Nairobi.