Reviews of A Very Long Engagement applaud Japrisot's skill in creating an intriguing mystery and the many ways in which he evokes the devastation caused by World War I. A Publishers Weekly critic praises Japrisot's "eloquently easy, almost offhand style," and comments that his "re-creation of the nobility, futility and horror of trench warfare is harshly beautiful." The critic has one reservation, however, and that is the character Mathilde, whom the critic finds difficult to like.

Christine Donougher in the Times Literary Supplement admires the way in which the novel places ordinary people at the center of events. The effect, Donougher argues, is to make the reader aware that the noncombatant survivors of the war— wives, girlfriends, parents, children, and neighbors—were just as much victims of the war as the men who fought and died. Although Donougher feels the unsentimental tone of the novel is sometimes forced, she concludes that it is a "cleverly constructed detective novel, with strong elements of suspense and surprise, and, at the same time, it conveys the high price which was paid for a war that seemed to produce no victors."

A New Yorker contributor observes that "Japrisot writes with warmth, and has a gift for rendering almost every character instantly likable." Rachel Billington in the New York Times Book Review finds some elements of the plot unconvincing, but has high praise for the style exhibited by Japrisot and his translator Linda Coverdale, which is "deceptive, apparently without flourishes but rich in imagery and daringly abbreviated rhythms."