Each of Ikea's 30 local markets around the world will now choose either a Group M or a Dentsu Aegis agency to handle its media buying.
It opens up the possibility that Ikea could conduct a six-way pitch between Group M’s four agencies, Maxus, MEC, MediaCom and Mindshare, and Dentsu Aegis’s two media agencies, Carat and Vizeum, in some markets.
However, while up to six agencies might be invited to respond to an initial request for information, it is more likely only four agencies or fewer would take part in a pitch.
Most of Ikea's local markets are expected to conduct media reviews in the next six months, including the UK and US.
Insiders believe it could be a first in the ad industry for an advertiser to appoint two media-buying groups as its global partners and then leave it up to each local market to pick its preferred agency.
Ikea selected Group M and Dentsu Aegis as part of a consolidation after a competitive pitch, which also involved Publicis Media and IPG MediaBrands.
Agencies from those four media-buying groups currently work for the Swedish furniture giant in different markets and the groups were all invited to take part in the global pitch. Ikea currently uses Vizeum in the UK and MEC in the US.
It is thought that Ikea's plans initially caused surprise because media-buying groups are used to an advertiser picking just one or two media agencies or one media-buying group on a global basis.
It is unusual to appoint two media-buying groups and then give significant autonomy to each market to pick its agency.
However, Ikea is privately owned and is said to be willing to challenge the status quo.
In a statement, Ikea said: "As part of our commitment to the ongoing improvement of our media and marketing governance, Ikea periodically evaluates all marketing service suppliers to ensure we maintain the best working relationships with the best agency partners.
"Ikea started this current global review process in April 2016 with the help of our strategic media consultancy partners, ID Comms, and our media audit partner, MediaPath.
"After our search and having received four very strong strategic proposals, we are pleased to announce we will be working with both Group M and Dentsu Aegis."