According to historian Paul Fussell, "In Flanders Fields" was the most popular poem of its era. McCrae received numerous letters and telegrams praising his work when he was revealed as the author. The poem was republished throughout the world, rapidly becoming synonymous with the sacrifice of the soldiers who died in the First World War. It was translated into numerous languages, so many that McCrae himself quipped that "it needs only Chinese now, surely". Its appeal was nearly universal. Soldiers took encouragement from it as a statement of their duty to those who died while people on the home front viewed it as defining the cause for which their brothers and sons were fighting.
It was often used for propaganda, particularly in Canada by the Unionist Party during the 1917 federal election amidst the Conscription Crisis. French Canadians in Quebec were strongly opposed to the possibility of conscription, but English Canadians voted overwhelmingly to support Prime Minister Robert Borden and the Unionist government. "In Flanders Fields" was said to have done more to "make this Dominion persevere in the duty of fighting for the world's ultimate peace than all the political speeches of the recent campaign". McCrae, a staunch supporter of the empire and the war effort, was pleased with the effect his poem had on the election. He stated in a letter: "I hope I stabbed a [French] Canadian with my vote."
The poem was a popular motivational tool in Great Britain, where it was used to encourage soldiers fighting against Germany, and in the United States where it was reprinted across the country. It was one of the most quoted works during the war, used in many places as part of campaigns to sell war bonds, during recruiting efforts and to criticize pacifists and those who sought to profit from the war. American composer Charles Ives used "In Flanders Fields" as the basis for a song of the same name that premiered in 1917. Fussell criticized the poem in his work The Great War and Modern Memory (1975). He noted the distinction between the pastoral tone of the first nine lines and the "recruiting-poster rhetoric" of the third stanza. Describing it as "vicious" and "stupid", Fussell called the final lines a "propaganda argument against a negotiated peace".