Barette, who most recently headed up new business but has also held senior consumer and creative roles, has left without a job to go to after six years at the agency.
Her departure follows shortly after the exit of Gallucci and the promotion of Dominic Shales to co-run the business with chairman Stephen Woodford.
Shales told PRWeek: "It’s always difficult to make these sorts of decisions, whoever is involved. We’ve been looking at the shape of the agency and what was becoming obvious was that the role of head of business development wasn’t needed at such a senior level."
He added that he was planning to make "seven or eight" hires to bolster the agency's junior to mid-ranking staff.
Barette had previously worked at Lexis for two years as creative director between 2004 and 2006. She rejoined the agency after time at Engine-owned Slice and having headed consumer PR at mobile phone operator Three.
She said: "After a total of eight thoroughly enjoyable years at Lexis, I wish the agency every success for the future."