[1] Nicholls adapted his book into a screenplay; the feature film, was released in August 2011, and a television series for Netflix, premiered on 8 February 2024.

Emma tries to overcome her problems and begins to write, while Dexter is unemployed and overwhelmed by his role as a father after his divorce from Sylvie, who was having an affair.

Visiting Emma in Paris, Dexter learns that she has met someone else, and for the first time admits his feelings to her.

Nicholls recalls that as a student, he read a passage in Thomas Hardy's 1891 novel Tess of the D'Urbervilles in which Tess realises that as well as birthdays and anniversaries "there was yet another date, of greater importance to her than those; that of her own death...a day which lay sly and unseen and among all the other days of the year, giving no sign or sound.

"[3] A critic in The London Paper observes that One Day "may be a love story, but it's no fairytale: Nicholls doesn’t shy from the harsh side of growing up, the disillusionment, regrets, and random cruelty of life.".

[4] According to Jonathan Coe, writing in "Guardian Books of the Year" (2009), "It's rare to find a novel which ranges over the recent past with such authority, and even rarer to find one in which the two leading characters are drawn with such solidity, such painful fidelity, to real life.

Writing in The Guardian, Harry Ritchie called it "a very persuasive and endearing account of a close friendship – the delight Emma and Dexter take in one another, the flirting and the banter that sometimes hide resentment and sometimes yearning, the way the relationship shifts and evolves as the years pass.

"[6] Ritchie comments, "Just as Nicholls has made full use of his central concept, so he has drawn on all his comic and literary gifts to produce a novel that is not only roaringly funny but also memorable, moving and, in its own unassuming, unpretentious way, rather profound.

Elizabeth Day of The Observer also praises the novel, although criticising "its structural flaws", since "some of the most important events in their life are never recounted."

"[7] The Times deflected comparisons to When Harry Met Sally..., "saccharine" assumptions, and expectations that the "more literary" will snobbishly gratify themselves that they never read "'commercial' romantic comedies with cartoons and squiggly writing on the cover.

It's also, with its subtly political focus on changing habits and mores, the best British social novel since Jonathan Coe's What a Carve Up.

"[3] Author Nick Hornby also praised the book on his blog, calling it "A big, absorbing, smart, fantastically readable on-off love story."

The writing team for the series was to be headed by Nicole Taylor, working with Anna Jordan, Vinay Patel and Bijan Sheibani and the series was to be produced by Drama Republic, Universal International Studios and Focus Features.