"There are plenty of things that were once commonplace that are now illegal, such as smoking inside.
"We know that the top 3000 companies in the world are responsible for more than £1.5 trillion worth of damage to the environment with meat and dairy production high on the list.
"It is time for a new law on ecocide to go alongside genocide and the other crimes against humanity."
Mansfield made his comments before a debate on how veganism can help protect the planet, at the Labour Party Conference in Brighton.
The world's top three meat producers are responsible for more greenhouse gases each year than all of France. Around 25 per cent of all greenhouse gases come from agriculture, with livestock farming contributing to 80 per cent of the total.
Juliet Gellatley, director of Viva!, a pro-vegan charity, said: "Thirty years ago people didn't bat an eyelid if you lit a cigarette in a pub or restaurant.
"But now society accepts smoking is harmful and totally unnecessary and so we legislated against it. The same could happen with eating meat.
"The global livestock industry is wrecking our most precious flora and fauna. And for nothing more than corporate greed.
"It's high time we kicked meat and dairy into touch and went vegan now."
The international crime of ecocide was originally proposed in 1970, at the Conference on War and National Responsibility in Washington DC, by Arthur Galston, a biologist who discovered that America's use of Agent Orange in the Vietnam War had caused devastation to wildlife.
Ecocide was initially included in early drafts of the Rome Statute, which laid out the remit of the International Criminal Court (ICC) but it was removed in 1996, following objections from Britain and the US.
Now the widespread destruction of wildlife can only be prosecuted if it happens during war.
Mansfield added: "I have one singular message: to make ecocide an international crime.
"Ecocide was going be a crime, but two nations objected: the United Kingdom and the United States.
"It ties in exactly with veganism, the rights of the animals, the rights of the environment, and the rights of human beings in one package."