She joins this week from InVentiv Health’s medical education house, Litmus, and at Just will lead a five-strong team of directors.
Mearns will also head up the agency’s medical education offer, which currently accounts for 20 per cent of agency business.
The agency has been led by founders Jennie Talman and Emma Crozier since its inception, and they have created the MD role to take over the operational running of the business to allow them to focus on strategy.
Mearns will be supported by director Jo Hewitt who will work with her on the expansion of the medical education capability.
Just has also promoted Jon Spiers to lead the agency’s political relations team, which accounted for 12 per cent of agency business in 2013.
This follows the recent hire of Catherine Barnett as a director with a focus on global stakeholder engagement.
Other directors are Laura Chambers, who is head of UK PR, and Julia Kirby, who has been instrumental in driving the growth of Just’s global business.