Spencer du Bois will be in charge of building the charity's brand awareness, while Whitewater will handle mailing communications for the organisation's donor campaigns.
Sherine Krause, MS Society's director of fundraising and marketing, said: "We have set ourselves some ambitious plans for raising awareness of MS and the MS Society's work. We are dedicated to alleviating the symptoms of MS for the 85,000 people in the UK affected by this devastating condition.
"Whitewater and Spencer du Bois share unrivalled expertise in producing results-driven fundraising and building sustainable awareness campaigns for charity clients."
Max du Bois, executive director of Spencer du Bois, said: "Having designed the logo some six years ago we are thrilled at the chance of working with the MS Society to help them build an effective brand and drive the organisation forward."