The agency will now take on all the print, outdoor and TV advertising for the Swedish furniture manufacturer.
BMB secured the business in June 2007 following a shootout against Wieden & Kennedy and Mother.
The agency's appointment marked a return to British agency's for Ikea, which had been using the Danish agency RBLM since 2005.
Previously the account was handled by Karmarama.
BMB's most recent campaign for Ikea, entitled 'Dumped', featured a man returning home from to find that his wife had not only made over their home thanks to the new Ikea catalogue, but had also traded him in for a different model.
BMB's Andrew McGuinness said: "We've struggled long & hard to help Ikea rediscover its voice. It's a great brand that deserves great ideas and we hope they find them at Mother."
Anna Crona, director of marketing at Ikea, said: "We have very big plans for our brand and business in the UK and Ireland and want to have the best creative partner on board to help realize our ambitions.
"We have known Mother for some time and are excited about what they can bring to our business."
Stef Calcraft, Partner at Mother, said: "Ikea is not only an iconic brand it is a truly inspiring business. It represents a treasure trove of creative opportunity and we are hugely excited at the prospect of combining Mother's full range of skills and talents with those of Ikea."
Mother's appointment follows that of Cake and Vizeum, who were handed the PR and media planning and buying accounts respectively at the end of last year.