Lawrence will sit on the same creative, commercial and executive management boards as her predecessor.
Duncan's job, officially known as the director of marketing, communications and audiences, has not been advertised yet, according to the BBC.
BBC marketing executives believed to be in with a chance include: head of communications, Sally Osman; controller of television strategy and marketing, Jane Scott; and controller of audience and research analysis, Chris Munday.
Duncan was appointed as Channel 4's chief executive on July 1 and he leaves the BBC tomorrow to take up his new role at Horseferry Road in London's Victoria.
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