Advertisers rarely review creative and media simultaneously or use two agencies under the same ownership, but observers said it could encourage integration.
One source involved said: "Asda has bought an integrated proposition. Physical proximity between creative and media teams is what the client is looking for."
Magnus Djaba, the UK chief executive of Saatchi & Saatchi Fallon group, will lead the integrated business.
Asda stunned the incumbents, VCCP and Carat, by moving the accounts – worth an estimated £95 million in billings – without a pitch. Carat had overseen Asda’s media for more than 20 years.
It is thought that Asda decided against a pitch as it wanted to move fast amid falling sales. An insider suggested this could become a trend, after Tesco moved its creative business to Bartle Bogle Hegarty also without a pitch.
Saatchi & Saatchi held Asda’s ad business until 2013. The network also handles creative for Walmart, Asda’s owner, in the US.