As well as devising the campaign's PR strategy, Global Tolerance will advise the three-strong internal press team on implementing a number of planned stunts and events ahead of the election on 1 May. The agency specialises in working with religious and ethical clients.
Agency founder and MD Simon Cohen said a key priority would be to raise Berry's personal profile by positioning her as an ordinary young Londoner, separate from the 'celebrity-oriented' London political scene.
He added: 'We want to show that the Green Party is interested in a range of issues including sustainability, transport, policing and affordable housing'.
Berry will be arguing that a greener London is a more affordable one. 'She wants to show that you do not need to be loaded to be green,' said Cohen.
The campaign team will mainly focus on the broadcast media, but will also expand the campaign's use of social networking.
Cohen identified The Guardian, The Independent and The Daily Mirror as priority press for the campaign. Berry currently writes a blog for the New Statesman.
Meanwhile, Conservative mayoral candidate Boris Johnson is preparing to spend up to £1m on his battle to oust Ken Livingstone as Mayor of London, it was reported this week.
The Australian election guru Lynton Crosby, who masterminded the Tories' 2005 general election campaign, was recently hired to oversee the campaign and Johnson is thought to be planning to unveil a string of high profile advisers during the coming weeks to counter his image as gaffe-prone.
Labour will also pour resources into the drive to keep Livingstone in office, and his campaign is one of the party's top priorities.