Along with Environment Secretary Owen Paterson they will tell delegates from around the world that the trade presents a grave threat not only to the natural world, but also to global security.
The conference will hear that both black and white rhino are coming under unprecedented attack, fuelled by demand for their horns.
Wildlife experts believe demand for ivory means that for the first time certain populations of African elephant face extinction within a decade.
Delegates at St James's Palace will be told that what used to be called "poaching" must now be called "trafficking" due to growing evidence that the trade is being driven by international organised criminal networks and, in some cases, terrorist and rebel militia groups.
Representatives from crime fighting organisations including Interpol, the United Nations Office on Drugs and Crime, WWF, Wild Aid and Traffic will be at the conference to discuss how to combat the problem.
The Prince of Wales will deliver a speech and the Duke of Cambridge will give a presentation.
As a patron of conservation charity the Tusk Trust, Prince William travelled with Prince Harry to Botswana in 2010 to raise awareness of the work being done.
In March 2013 he sent a video message to the Convention on International Trade in Endangered Species of Wild Fauna and Flora in which he said: "We need to do more to combat this serious crime if we are to reverse the current alarming trends.
"If not, we could soon see some populations of these creatures or even an entire species disappear from the wild. We simply must not let this catastrophe unfold."
Earlier this year Sky News filmed in the Kruger National Park in South Africa where rhino are targeted by poachers.
In one case, a horn had been cut from an animal that was still alive.
Gamekeepers there say they are fighting a losing battle.
In the UK, at Chester Zoo, ten critically endangered eastern black rhino are kept and bred.
It is estimated that fewer than 650 now exist in the wild. The population has declined by more than 95% since 1960.
On the black market, rhino horn sells for around £60,000 per kilogram - twice the value of gold.
Scott Wilson, a conservationist at Chester, said poaching is being fuelled by an increased demand for rhino horn and ivory.
He told Sky News: "There's an increase in demand in places like China and Vietnam. People are becoming wealthier in those countries so more people can afford the products.
"In the countries where it's used, people believe it has medicinal properties, from helping cure a hangover to cancer. None of this has been proven."
It is hoped that the conference will be the first stage in a process which will result in key countries signing a declaration at a meeting in the autumn to commit at the highest levels to end the illegal trade in wildlife.