The animal welfare charity called in Bright Young Things following a competitive pitch. The agency will look to secure high-profile support for the ban, which could be over-turned if the Conservatives win the general election.
Party leader David Cameron said in October that a Tory government would give MPs a free vote on a repeal of the hunting ban.
However, Bright Young Things MD Niall Cowley insisted the agency's appointment was not related to Cameron's announcement.
A new campaign, called 'Keep Cruelty History', will see celebrities joining forces to call on all parties to listen to what the public has to say about the hunting ban. The charity says the majority of the public want the ban to stay.
The agency will be supporting the league's press office by securing major celebrities to front the campaign throughout 2010. It also aims to produce 'cutting-edge' viral videos to reach younger audiences.
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.
Last month, Environment Secretary Hilary Benn announced that he was launching a campaign to boost support for the ban. He said: 'Like the majority of people, I believe the barbaric act of letting dogs tear foxes to pieces should not 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 Tory government would consider creating a regulatory body for fox hunting, which could work towards 'minimising animal suffering'.