Mergenthaler invented and perfected linotype, the first automated typesetting machine, which proved to be an invention largely responsible for the publishing boom in the first half of the twentieth century.

Born in Hachtel, Germany,on May 11, 1854, Mergenthaler was apprenticed to a watchmaker at the age of fourteen, but his true interest was in engineering. After emigrating to the United States in 1872 to avoid military conscription, Mergenthaler went to work in a relative's machine shop in Baltimore, Maryland; there, he became interested in printing technology after being approached to build a model of an automatic typesetting machine for another designer. The model failed, but the concept intrigued Mergenthaler.

There had been no real advances in the typesetting process since Johannes Gutenberg 's introduction of movable type; typesetters still selected cast-metal letters and punctuation from a prepared stock to piece together full pages by hand. Although earlier inventors had conceived machines that would piece together type into pages, their inventions were not efficient enough to be marketable.

Mergenthaler abandoned the basic concept behind these attempts. What typesetters needed, he reasoned, was not a machine that would take over the slow, jigsaw puzzle-like process; they needed a new process altogether. Mergenthaler conceived of a machine which would custom-make a mold of letters that could be inked and pressed onto paper. He experimented with various unsuccessful models, including a machine that would punch letters into papier-mâché to create a mold; then he hit upon the technique that would become linotype. He designed a machine with a keyboard that moved pre-cast copper letter and punctuation molds into a line, over which it poured a quick-cooling alloy that became a line of finished type. Mergenthaler patented linotype in 1884; soon after, he modified it to automatically justify text, or insert spaces between words so each line is exactly the same length.

In 1886, The New York Tribune became the first newspaper to use linotype. Mergenthaler set up a company to market linotype but resigned in 1888 over disputes with his partners. Nonetheless, he continued to develop and patent refinements to his machine for the rest of his life. By his death on October 28, 1899, in Baltimore, more than three thousand linotype machines were in use around the world.