Derbyshire's immediate task in her new role will be to deliver a nationwide experiential campaign for the current 'Do us a flavour' Walkers Crisps campaign.
She will also work with clients including Nike, NFL, Aviva, BMW and Famous Grouse.
Derbyshire joins Not Actual Size from Sledge where she was the senior account director on the Innocent Village Fete account, running the fete in Regents Park, as well as its regional tour across the UK.
This role involved managing a team of people to deliver an event for 60,000 Londoners from concept to activation in 12 weeks.
Derbyshire began her career as a graduate trainee at Proximity working on accounts including The Economist and Shell.
Following a two-year stint there, she moved on to Iris where she worked on a range of accounts including Sony Ericsson, Budweiser and Coca Cola.
Dan Holliday, managing director of Not Actual Size said, "We are constantly on the lookout for people with strong expertise in all areas of marketing, and Laura has been an integral part of some of the best experiential campaigns bar none."
Holliday launched Not Actual Size in May 2007 with the agency's director Amy Hitchenor.