Jim Hodkinson, 53, will leave the group at the end of April and will not receive a pay-off. He plans to make an announcement about his new venture next week. "It is in an area which does not compete with any of the Kingfisher businesses and we will be announcing the details shortly," he said.
Given the spread of Kingfisher's interests, analysts said it must be fashion or food retailing. There were rumours that Mr Hodkinson might be joining Safeway, the struggling supermarket group, but the company denied it.
It is the second time Mr Hodkinson has left the company. In 1995 he quit to join American DIY group Home Depot which was then considering entering the UK market. He came back to B&Q when the Home Depot changed its mind.
He said yesterday: "I'm sad to be going really. I've got a lot of good feelings about B&Q. I came back to turn the business round and I think people would say I have done that. It is just the right time for me now and it's nice to go out on a high."
Kingfisher shares dipped 18p to 1120p on the news but analysts said that though Mr Hodkinson was highly regarded, the two joint managing directors - Martin Toogood and Bill Whiting - were a good team. "I think the share price fall is a bit churlish. It is all a storm in a teacup," said Nick Bubb of SG Securities.