Howe has promoted the head of ideas, Alistair Ross, to head of creative to replace Fiddes, who had worked at the agency for three years. And she has drafted in DDB UK's deputy head of planning, Vicki Holgate, as the head of planning.
Ross and Holgate will work alongside DraftFCB's chief operating officer, Mark Young, and its president digital, Martin Talks, in Howe's first management restructure since taking the reins in 2009.
Ross takes charge of DraftFCB's 20-strong creative department. He joined the agency in 2010 from VCCP, where he was the integrated creative director on O2, and was previously at Publicis, where he was responsible for campaigns for the Army.
Holgate replaces the global chief planning officer, Simon Calvert, who left in January after two years to join Digitas as the worldwide head of strategic planning. She has also worked at Grey and JWT.
In her new role, Holgate will oversee the agency's planning department of around 16 people, including Phil Nunn, DraftFCB's new global communications architect.
Howe said: "I'm very happy to announce Alistair's well-deserved promotion and the addition of Vicki to our DraftFCB team. They both have an undeniable passion in their respected fields and share similar visions of advertising and the industry at large."
Before joining DraftFCB in 2009, Fiddes was the global creative director at Euro RSCG Worldwide.