Sarah Leaman had been at the supermarket for three years until her departure in December, reporting to director of comms Pip Wood.
She will now work on expanding new business for Cirkle, as well as building the agency's reputation with key external stakeholders and leading its client and media satisfaction audits.
Before working for Sainsbury's, Leaman was consultant director at Euro RSCG Biss Lancaster.
Sainsbury's recently poached Hill & Knowlton's consumer MD, Rachel Friend, to replace Leaman (PRWeek, 23 February). Friend, who was at H&K for nine years, now heads the in-house press team at the supermarket.
Cirkle has a wide range of fmcg clients, including Walkers, Lucozade and Tropicana. It recently opened a new division, Body + Soul, focusing on grooming, fitness and wellbeing products.