Before 1902: Chicago and Paris
As a staff artist at J. Manz & Company J. C. Leyendecker produced 60 Bible illustrations for the Powers Brothers Company, cover and interior illustrations for The Interior magazine, and frontispiece art for The Inland Printer. He also produced artwork for posters and book covers for the Chicago publisher E. A. Weeks. From ca.1895-1902, he provided artwork for the marketing materials of the Chicago men's clothier Hart, Schaffner & Marx.
While in Paris, J. C. Leyendecker continued providing art to Hart, Schaffner & Marx, produced artwork for 12 covers of The Inland Printer, and won a contest (out of 700 entries) for the poster and cover of the midsummer 1896 issue of The Century Magazine, which garnered national newspaper and magazine coverage.
Upon his return from Paris in June 1897, Leyendecker illustrated for a range of mostly local clients including Hart, Schaffner & Marx, the Chicago department store Carson, Pirie & Scott, the Eastern Illinois Railroad, the Northern Pacific Railroad, Woman's Home Companion magazine, the stone cutter's trade journal Stone, Carter's monthly, the bird hobbyist magazine The Osprey, and books including Conan Doyle's Micah Clarke and Octave Thanet's A Book of True Lovers. He also painted 132 scenes of America for L. W. Yaggy's laptop panorama of Biblical scenes titled Royal Scroll published by Powers, Fowler & Lewis (Chicago).
During the 1890s, Leyendecker was active in Chicago's arts community. He exhibited with and attended social events by the Palette and Chisel Club, the Art Students League, and the Chicago Society of Artists. In December 1895, some of his posters were exhibited at the Siegel, Cooper & Company department store in Chicago. In January 1898 his posters for covers of The Inland Printer were exhibited at the Kimball Cafetier (Chicago).
During his 1895–97 time studying in Paris, J. C. Leyendecker's work won four awards at the Académie Julian and one of his paintings titled "Portrait of My Brother" was exhibited in the Paris Salon in 1897. One of his posters for Hart, Schaffner & Marx titled "The Horse Show" was exhibited as part of the award-winning display of American manufacturers' posters at the Exposition Universelle (1900) in Paris.
Leyendecker's first cover illustration for The Saturday Evening Post was published in its May 20, 1899 issue, launching a forty-four-year association with the magazine. Eventually, his work would appear on 322 covers of the magazine, introducing many iconic visual images and traditions including the New Year's Baby, the pudgy red-garbed rendition of Santa Claus, flowers for Mother's Day, and firecrackers on the 4th of July.