Mather joins from entertainment and media consultancy BBH London, where he held a number of roles including head of account management and business director. He played a key role in retaining the British Airways business through a lengthy repitch process before leaving the agency in July.
Exposure founders Raoul Shah and Tim Bourne remain joint CEOs of the global group, which operates in London, New York and Tokyo with a team of 200 PR professionals.
Bourne said: "The appointment of Keir to the UK MD position is one of the most significant developments in our 20-year history. Keir brings a wealth of experience from an agency we have always admired and respected. We’re delighted to have him on board to lead Exposure through a new and exciting phase of growth.
"Aligning our various specialisms, deepening our pillar client relationships and supporting our stellar growth in digital will all require the expertise and skills of an individual like Keir. He is a great cultural fit for Exposure with an appetite for success and building organisational excellence."
The Exposure group consists of brand innovation consultancy The Gild, lifestyle communications agency Three Sixty, PR and marketing agency Beauty Seen, digital agency Exeat and research and analytics agency eQ.
Mather said: "Exposure is an agency that has more than 20 years of experience in making brands culturally relevant. The agency has evolved incredibly and organically throughout its history to meet the client needs in an increasingly complex communications landscape."