After his father’s death in 1824, Daniel, aged 11, was apprenticed to a bookseller in Irvine, Scot.; he moved to Glasgow, Scot., in 1831 and to Cambridge, Eng., two years later. From 1837 to 1843 he worked for Messrs. Seeley, London booksellers, and then bought out a bookshop in Cambridge, where he was joined by his brother Alexander; their first catalog appeared in March 1844. The Macmillan & Co. bookshop prospered, and within two years the brothers had absorbed the business of their chief local rival. The Macmillans began publishing textbooks in 1844, met with steady success, and published their first novel, Charles Kingsley’s Westward Ho!, in 1855. Their first best-seller was Thomas Hughes’s novel Tom Brown’s School Days (1857).
At the time of Daniel’s death in 1857, the firm was still rather small, issuing about 40 titles annually. Alexander expanded the list to more than 150 annually during his 32 years of active management; he founded Macmillan’s Magazine (1859–1907), a literary periodical, and Nature (1869 to date), which became a leading scientific journal. In 1867 he visited the United States to establish a branch office; the U.S. company was sold in 1951 but retained the Macmillan name. Alexander also expanded its activities to Canada, Australia, and India.
Frederick Orridge Macmillan, the son of Daniel, became a partner in 1876 and first chairman in 1893. Frederick’s partners were his younger brothers Maurice Crawford and George Augustin Macmillan; they were succeeded by Maurice’s sons Daniel de Mendi Macmillan, the chairman, and Harold Macmillan, who, in a reorganization of the company in 1964, became chairman of Macmillan & Co., the book-publishing side of the business. The Macmillan family formally ended its ownership in 1999, when the German media group Verlagsgruppe Georg von Holtzbrinck GmbH completed its acquisition of all the company’s shares. In the early 21st century, Macmillan had offices in more than 40 countries. Its headquarters are in London.
According to britannica.com