Saturday was both critically acclaimed and commercially successful, a best-seller in Britain and the United States. It spent a week at No. 3 on both the New York Times Best Seller List on 15 April 2005, and Publishers Weekly (4 April 2005) lists. A strong performance for literary fiction, Saturday sold over 250,000 copies on release, and signings were heavily attended. The paperback edition sold another quarter of a million.
Ruth Scurr reviewed the book in The Times, calling McEwan "[maybe] the best novelist in Britain and is certainly operating at the height of his formidable powers". She praised his examination of happiness in the 21st century, particularly from the point of view of a surgeon: "doctors see real lives fall to pieces in their consulting rooms or on their operating tables, day in, day out. Often they mend what is broken, and open the door to happiness again." Christopher Hitchens said the "sober yet scintillating pages of Saturday" confirmed the maturation of McEwan and displayed both his soft, humane, side and his hard, intellectual, scientific, side.
Reviewers celebrated McEwan's dissection of the quotidian and his talent for observation and description. Michiko Kakutani liked the "myriad of small, telling details and a reverence for their very ordinariness ", and the suspense created that threatens these. Tim Adams concurred in The Observer, calling the observation "wonderfully precise". Mark Lawson in The Guardian said McEwan's style had matured into "scrupulous, sensual rhythms," and noted the considered word choice that enables his work. Perowne, for example, is a convincing neurosurgeon by the end of the book. This attention to detail allowed McEwan to use all the tricks of fiction to generate "a growing sense of disquiet with the tiniest finger-flicks of detail".
The "set-piece" construction of the book was noticed by many critics; Mrs Scurr praised it, describing a series of "vivid tableaux", but John Banville was less impressed, calling it an assembly of discrete set pieces, though he said the treatment of the car crash and its aftermath was "masterful", and said of Perowne's visit to his mother: "the writing is genuinely affecting in its simplicity and empathetic force." From the initial "dramatic overture" of the aircraft scene, there were "astonishing pages of description", sometimes "heart-stopping", though it was perhaps a touch too artful at times, according to Michael Dirda in The Washington Post. Christopher Hitchens said that McEwan delivered a "virtuoso description of the aerodynamics of a squash game," enjoyable even "to a sports hater like myself", Banville said he, as a literary man, had been bored by the same scene. Zoe Heller praised the tension in the climax as "vintage McEwan nightmare" but questioned the resolution as "faintly preposterous".
John Banville wrote a scathing review of the book for The New York Review of Books. He described Saturday as the sort of thing that a committee directed to produce a 'novel of our time' would write, the politics were "banal"; the tone arrogant, self-satisfied and incompetent; the characters cardboard cut-outs. He felt McEwan strove too hard to display technical knowledge "and his ability to put that knowledge into good, clean prose".
Saturday won the James Tait Black Prize for fiction; and was nominated on the long-list of the Man Booker Prize in 2005.