The agency will promote its year-long fundraising campaign in support of the Lord Mayors charities.
The campaign will benefit St John Ambulance London (Prince of Wales's) District and The Lord's Taverners. Edelman will publicise individual fundraising events, as well as raise the profile of both charities more generally.
The Appeal will be chaired by Stanley Fink, the former chief executive of hedge fund Man Group, who is also represented by Edelman.