Brunton founded Welbeck PR alongside chairman Denis Inchbald.
Welbeck, originally the PR department of FCB advertising, was acquired by Shandwick in 1986.
She remained as managing director of the agency until her retirement in 1998.
Alison Clarke MPRCA, PRCA 2012-2014 chairman and Grayling UK CEO, said: "Ann will be sadly missed. She was instrumental in nurturing the careers of many in the industry today and will be known for some of the high profile campaigns she ran, including the Miss Pears Competition."
Brunton was an active member of the PRCA.