His departure at the end of this month follows the summer merger with French DIY company Castorama-Dubois and a subsequent restructure of all departments, which is due to end next year.
The restructure of comms has been completed and has seen the scrapping of the directorate of corporate affairs.
Head of external communications Jonathan Miller said: 'His (Mills) role ceased to be. He worked with the company to see if there were other opportunities within the company but he has decided to pursue his career elsewhere.'
In the new structure Mills' roles in City PR and media relations are taken over by a six-strong directorate of financial comms headed by former IR director, now director of financial comms Ian Hardy.
Public affairs and CSR are now part of a new directorate of governance and corporate services, which also includes the functions of the now defunct company secretariat.
The changes come as Kingfisher, which owns the B&Q chain, continues its repositioning as a DIY specialist, having disposed of most of its non-DIY businesses.