Alongside Tash Whitmey, the group chief executive, Whitcombe will lead the Havas Helia agencies in London and Cirencester.
David Williams, the managing director at Havas Helia Cirencester, has been promoted to group chief operating officer.
Matt Fanshawe, the former chief operating officer and managing director in London, departed last year.
Whitcombe first joined the M&C Saatchi-owned Lida in May 2011 and left in 2012, when she was its deputy managing director. Whitcombe returned to the shop in 2013.
Between the two stints, she worked at Bartle Bogle Hegarty as its CRM director.