W&K triumphed this week after a six-month pitch process. The decision deals a blow to The Red Brick Road, which had emerged as the early favourite in the pitch because of the relationship established with The Guardian by Paul Hammersley.
Hammersley, a founder of The Red Brick Road, worked on the business during his time as the chief executive of DDB London.
DDB, which had held The Guardian account for the past five years, declined to repitch for the business.
Marc Sands, the marketing director at Guardian Newspapers, said that the new work will be a departure from the newspaper's recent "think" campaign.
The new creative approach will relaunch The Guardian as a multimedia brand and is due to launch early next year. Neil Christie, the managing director of W&K, said: "It's going to be a relaunch of the Guardian brand and what it stands for in a digital age."
Sands said: "Over-assertive endlines and ridiculous claims don't really work. It has got to be a true reflection of what The Guardian is."
He added: "You will not be able to tell where the newspaper ends and the marketing begins."
W&K won the business in a final shootout with The Red Brick Road, after Fallon was eliminated from the process. VCCP withdrew from the contest over potential conflict with its Metro client.
The Guardian, which enjoyed a 3.4 per cent year-on-year rise in its circulation to 370,600 in July, has more on- than offline readers: its website had nearly four million unique users in the UK in June.
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