Laura Osborne will leave Which? ahead of Cool's arrival. Previously head of corporate affairs, she had led the comms function on an interim basis since February 2017.
Cool previously spent just over a year as vice president of corporate affairs at Asda, before which she was John Lewis Partnership's group head of corporate affairs for a decade.
At Asda, she ended the retailer's longstanding relationship with Freuds not long after joining, but left in Autumn 2017 following a major redundancy round at the firm. Cool had joined shortly before then-Asda CEO Andy Clarke left the business.
At Which?, Cool will have a team of around 60 working for her, two thirds of whom are in corporate comms, events, social, community engagement, press office and planning, while the remaining third are advocacy and external affairs specialists.
She said: "I'm delighted to be joining Which? as it celebrates its 60th anniversary, to help deliver its ambitious commercial and campaigning goals, and to empower consumers in new and diverse ways."
Cool also told PRWeek she was interested in widening the demographic and numerical reach of the organisation's output.
Prior to Osborne's interim stint, the previous comms lead was Vickie Sheriff, who spent six months in the role. Before that, the department was led by Alex Neill, who now has a more senior role in the business. In 2016, PRWeek interviewed Abbie Sampson, the head of news under Neill.