Moll is leaving the advertising industry to spend more time with her family.
The move comes after the agency reactivated the role of business development director in October, handing it to Clare Hornby. Moll, meanwhile, took on responsibility for some of HHCL's clients, including Bhs and COI Communications.
Jason Cobbold, HHCL's client services director, is now expected to take on these responsibilities.
Moll said: "It will be a real wrench to leave after ten years. HHCL is one of the real brands in the industry and I am proud to have served."