After working for Philip D. Armour (Armour, Philip Danforth)'s meatpacking company in Chicago (1887–95) and failing in his own wholesale grocery business, Lorimer went to Boston and became a newspaper reporter. When Cyrus H.K. Curtis (Curtis, Cyrus Hermann Kotzschmar) bought The Saturday Evening Post in 1897, he hired Lorimer as literary editor and then made him editor in chief. In 1932 Lorimer became president of the Curtis Publishing Company.

In the Post he published works by some of the best American writers of the time: Stephen Crane (Crane, Stephen), Frank Norris (Norris, Frank), Theodore Dreiser (Dreiser, Theodore), Jack London (London, Jack), Willa Cather (Cather, Willa), Ring Lardner (Lardner, Ring), F. Scott Fitzgerald (Fitzgerald, F. Scott), and Sinclair Lewis (Lewis, Sinclair). In addition, he brought such European authors as Joseph Conrad (Conrad, Joseph) and John Galsworthy (Galsworthy, John) to American readers. In 1916 Lorimer met the then-unknown artist Norman Rockwell (Rockwell, Norman) and put him to work as an illustrator; Rockwell's cover illustrations for the Post fed the magazine's success, and his own. It was sometimes believed, however, that he accidentally found excellence while seeking mere novelty; the poet Ezra Pound (Pound, Ezra) remarked (in Guide to Kulchur 【1938】) that “Lorimer honestly didn't know that there ever had been a civilization.”