She joins the BBC tomorrow (Wednesday) and will be responsible for magazines including BBC Good Food, BBC Good Homes, Toybox and Top of the Pops.
Dempster replaces Amanda Pitt, who left to join Eve when it was sold by the BBC to Haymarket in January, and adds the youth titles to Pitt's old responsibilities.
Dempster is one of six senior staff members who were recently told their jobs were at risk and put into a consultation period following a business efficiency drive by the French-owned publisher. Four people are still in consultation and two, Clare Bull and Sarah Vickery, have now left. Hachette Filipacchi told Media Week that Dempster was still in a consultation period and therefore remained under contract.
Meanwhile, Mary Langan, currently ad director for the key customer group, will take up the role of acting group ad director across the central revenue streams. She replaces Matt Teeman, who has taken over the role of director of advertisement sales at BBC Magazines until February 2006.
He is acting in this role on a temporary basis while current ad boss, Ashley Munday, is in India overseeing projects for BBC Worldwide's joint venture with the Times of India Group.
Teeman said: "Clare Dempster has a great reputation from her work at both Hachette and Emap, where she oversaw titles such as Red, Elle and Sugar."
Elsewhere, Dan Green is leaving his job at IPC Media as head of classified across its equestrian, marine and shooting titles, to become director for BBC Magazines' classified department on 3 January.
Green replaces Sarah Shelton. who has moved to Trinity Mirror to head its classified division.