The campaign aims to inspire people to make the most of London's parks, gardens, alfresco dining and outdoor events over the summer.
It launches on 27 May and runs until the end of July, with the tagline 'be a free range Londoner - discover London's great outdoors'.
As part of the campaign, people will be seen dressed as giant eggs in picturesque locations around the capital.
Cake account director Jude Forbes said: 'We'll be working closely with the London media to place stories about the parks and green spaces in London and the abundant wildlife. We are also working on an event for June.'
The agency is retained by Visit London. It receives public funding from the Department for Culture, Media and Sport via the Mayor of London and the London Development Agency and London councils.