As chief client officer, Hart has been tasked with leading strategic relationships across the media planning and buying network’s client base. She will report to Havas Media UK and international chief executive Matt Adams.
Hart joins from creative and technology agency MRY, after three-and-a-half years, and will be based in the new Havas Village in London’s King’s Cross.
She joined in September 2013 as executive client partner and head of client services, based in New York, before relocating to London in December 2014 to become managing director, Europe.
Before MRY, Hart had worked at LBI for five years – latterly as a client partner at LBI based in New York between 2011 and 2013 – and started her career as an account manager at Haymarket (the publisher of Campaign).
Adams, who was appointed as UK chief executive at Havas Media last September, has made a number of C-suite hires this year, including chief strategy officer Stuart Butler from WPP’s Maxus.
Hart joins Havas at a pivotal time for the French advertising company, which last month announced planning to merge its creative and media business divisions under one regional P&L, with Chris Hirst appointed UK chairman.
While Hart will oversee UK client relationships, Havas’ global managing director Dominique Delport is in charge of managing global clients.
Adams said: "At Havas we are committed to investing in top class talent, bringing in new firepower to support our clients, our thinking and our offering.
"In this newly created group role Clare will help us reinvent how brands tell stories in a digital world. She will oversee client leadership across the agency group to ensure we are client focused and committed to exceeding expectations in all areas of our agency offerings.
"Clare’s background in and passion for creativity and innovation makes her the perfect fit for the direction in which we are travelling here at Havas."