The agency, 442 Design, worked on the scheme as part of Historic Scotland's 500,000 overhaul of retail, ticketing and visitor facilities at the castle.
The courtyard gift shop, palace gift shop and Clan & Craft gift shop were all redesigned.
The scheme accompanied a 12 million refurbishment of the castle itself to return it to the way it may have looked in the mid-16th century.
Managing director David Dunn said: "The Stirling Castle retail project has been a fascinating creative and commercial challenge for our team.
"Working on the principle of reviving renaissance history, we aim to extend the fantastic visitor experience of the palace to the retail offering, and make it work in a commercial context.
"We are thrilled to have had this opportunity to work with Historic Scotland."