The British Ministry of Information commissioned the Keep Calm and Carry On poster between 27 June and 6 July 19395. It was one of three "Home Publicity" posters designed to boost civilian morale if Germany invaded Britain. The other two read "Your Courage, Your Cheerfulness, Your Resolution Will Bring Us Victory" and "Freedom Is in Peril / Defend It With All Your Might"4.

A civil servant named A. P. Waterfield contributed to the slogan development, and Ernest Wallcousins was the artist who created the poster designs5. The lettering was likely hand-drawn by Wallcousins in a style similar to Gill Sans and Johnston typefaces5. Almost 2.5 million copies were printed between 23 August and 3 September 1939, but unlike the other two posters, Keep Calm was held in "cold storage" for use only after serious air raids5. The land invasion never came, and most copies were pulped as part of Britain's Paper Salvage campaign by April 19405.

The poster sat in near-total obscurity for six decades. In 2000, Stuart and Mary Manley, owners of Barter Books in Alnwick, England, found an original copy folded at the bottom of a box of old books they'd purchased at auction1. Not knowing what they had, the couple framed it and hung it in their shop. Customers loved it, and the Manleys began selling reproductions. By March 2009, they had sold over 40,000 copies4.

The poster tapped into what Mary Manley described as "nostalgia for a certain British character, an outlook"1. That nostalgia turned out to be globally marketable. "Germany's really big on it, oddly enough," noted merchandise seller Mark Coop1.

But the poster's cultural story is more complicated than a straightforward tale of wartime British resolve. As Dr. Rebecca Lewis pointed out, "People talk about it, Americans in particular I'm afraid, being the poster that kept the British going through the war"1. In reality, almost no one saw it during wartime. The few similar posters that were displayed at the time actually drew criticism for their "condescending, authoritarian tone," and the government abandoned the stark look in favor of "a lot more colorful and a lot more people-focused" designs1.

Design historian Susannah Walker called the original poster campaign "a resounding failure," reflecting a misjudgement by upper-class civil servants of the mood of the people5. Mass Observation analysis of the public response was overwhelmingly negative, with some interpreting the "Your Courage" companion poster as implying common people would suffer for the benefit of the upper classes5.

The poster's influence extended into music when Stereophonics used it as an album title in 20094. Flickr hosted a community pool of nearly 500 design variations4. Collections of parodies were featured on BuzzFeed and other viral content sites2. The meme also made a mark on academic study, with Lewis's blog tracking hundreds of derivatives across media and commerce3.

Relations among the various sellers were not particularly friendly. The New York Times reported that each complained of copycats selling low-quality versions1.