[4] Agents Red and Blue travel back and forth through time, altering the history of multiple universes on behalf of their warring empires, whose timelines are mutually exclusive.

[5] Publishers Weekly called This Is How You Lose the Time War "exquisitely crafted" and "dazzling", with "increasingly intricate wordplay", and stated that it "warrants multiple readings".

[7] Cheryl Morgan argued that its central message—"soldiers on either side of a war often have far more in common with each other than they do with the people who sit safely at home and issue orders"—is one "that the world needs to hear".

"[10] At Strange Horizons, Adri Joy lauded the novel as "an absolute emotional masterpiece, sending readers on a gut-wrenching feelings rollercoaster of the highest calibre."

She noted that "the Time War itself [...] is largely incomprehensible beyond its most basic points", but specified that "every little aside of... description works to set the scene in the most effective possible way", including the "impermanence" of the messages delivered between Red and Blue.