The retailer is seeking a top-line sponsor to support the 18-month campaign, encompassing two Christmas selling periods, next autumn.
The drive will also include print, radio, online and direct activity, in-store events and promotional projects.
The theme of the work will be 'past, present and future'. Hamleys' head of marketing, Matt Webb, said the story would go 'beyond the parameters of retail', and hinted that it may involve an external theatrical production.
Once selected, Hamleys' top-line sponsor will be associated with every aspect of the anniversary campaign.
Webb said he would consider partnerships with a number of brands outside the toy industry including financial services, car manufacturers and drinks brands. The toy store is also looking for territory-specific media partners.