Mr Benn is urging people to sign up on a website backing the ban.
He claims the Tories plan to make repeal of the Hunting Act "a priority". Party leader David Cameron has promised MPs a free vote on the issue.
The pro-hunting Countryside Alliance has said Saturday's meets could be the last traditional Boxing Day hunts before the ban is repealed.
Jill Grieve, a spokeswoman for the campaign group, said more than than 200 hunts are being held across the UK on Boxing Day.
She said these events range in size and involve between 200 and 8,000 people.
Hunting foxes with dogs was outlawed in 2005, although hounds are still allowed to follow a scent or flush out a fox, but not kill it.
Mr Benn's campaign is being launched to coincide with the Boxing Day hunts and is backed by the actors Patrick Stewart, Jenny Seagrove and Tony Robinson.
The environment secretary said: "For David Cameron, getting the act repealed is a priority.
"He used to hunt foxes; he talked about fox hunting in his first ever speech to Parliament; and he has said that if he becomes prime minister he will get rid of the fox hunting ban.
"But, like the vast majority of people, I think that the barbaric act of letting dogs tear foxes to pieces shouldn't return to our countryside."
In October, shadow environment secretary Nick Herbert described the hunting ban as "an affront to civil liberties" and "completely unworkable".
He said a Conservative government would consider creating a regulatory body for fox hunting which could work towards "minimising animal suffering".
But Mr Benn insisted Mr Herbert and Mr Cameron's views were indicative of wider Conservative attitudes.
"If you think the Tories have changed, their views on fox hunting with dogs make it absolutely clear that their priorities haven't," he added.
Only a small number of prosecutions under the Hunting Act have reached court since 2005, but the League Against Cruel Sports says the arguments in favour of repeal "don't stack up".
The League Against Cruel Sports has released graphic footage which it says reinforces the need for a ban.
It says the footage, filmed before the act came into force, shows "the horrific cruelty" of hunting.
Chief executive Douglas Batchelor said: "The arguments in favour of repeal simply don't stack up and we believe the public has a right to see what the hunting lobby, and some politicians want to bring back.
"The truth of the matter is that hunting is barbaric and cruel and the only purpose it serves is to appease the sick minds of a very small minority who enjoy torturing animals for their own entertainment."
But the Countryside Alliance says the ban is "fundamentally illiberal, based not on principle and evidence but prejudice. Such laws should have no place in a modern, tolerant and free society."
It also insists: "The hunting community stands united and determined to secure repeal and huge support is anticipated this year."
Source. Benn's article on the ban in the Independent here; Independent talks about the class implications of the hunting ban here and here. The Telegraph, noted paper of the encrusted, ancient right, frothing xenophobes, and retired colonels with handlebar moustaches, thinks repealing the law is a bally good idea.
I went protesting against the local hunt this morning, I *actually* got called an 'oik' by a man with nicotine-stained hair and a million broken capillaries on his face. I'm genuinely curious to know what people, British or otherwise, think about this issue.