Harris, who has bought into the company, will be the joint chief executive alongside Nicola Stephenson who founded Mission ten years ago. Mission’s clients include Nokia, Matalan and Cath Kidston.
Harris started his career agency-side, working at Lowe Howard-Spink as a graduate trainee, before moving to WCRS and Abbott Mead Vickers BBDO.
However, most of his working life has been spent in telecoms marketing, notably overseeing the launch of the O2 brand, although he was also marketing director of the Conservative Party under the leadership of Michael Howard.
After leaving his role as head of marketing for Nokia South East Asia Pacific last year, he spent a short time as chief marketing officer for premium vodka brand Belvedere, also a Mission client.
Most recently Harris, a regular contributor to Marketing, has worked for WPP.
Reflecting on his move, Harris said he was "trying to bring the rigour and discipline of advertising to the flair and responsiveness of PR. If you can do that, I think there's huge potential for growth".
Harris added: "I'm interested in whether PR can be one of the new battlegrounds as the agency landscape reshapes itself. It's threatened by social and bloggers, but if you get it right, then the upsides are fantastic."
Asked why he had favoured the PR discipline when his background would suggest a move into advertising appeared more logical, Harris said: "At the top of an organisation, actually the job is pretty similar. My competency is ideas, you can do that anywhere."