The group will create a 'Team WBA' to service the business.
Finsbury partner James Murgatroyd told PRWeek that the agency would continue its "longstanding role" with the business - it had worked with Alliance Boots since 2008, prior to its merger with Walgreens - and that Burson-Marsteller and Ogilvy PR would also have a role.
However, it is unclear whether other WPP PR agencies, such as Cohn & Wolfe and Hill+Knowlton Strategies, will be involved in the partnership.
The partnership will see "more than 200 existing marketing and communications agencies and suppliers gradually transitioned" to a single agency model, said Yves Romestan, senior VP, communications and international affairs at WBA.
A core objective of WBA's "one agency model" is the development of a communications strategy that will create "significant brand equity" for the company.
This new comms model will be phased in and continuously developed over the coming months, Romestan said.
"It is because of its scale and territorial coverage, and therefore its ability to support any future expansion that WPP has been chosen as our partner in this venture."
WBA also wants to establish a new marketing a comms framework to improve agility, foster creativity, increase consistency and align and better connect global and local teams, Romestan added.
Walgreens and Alliance Boots merged in December 2014, following a deal worth a reported £16bn.