In 1819, Friedrich Wilhelm Harkort and Heinrich Daniel Kamp founded the Mechanical Workshop Harkort & Co. By the turn of the century, a company grew, which supplied many customers in Europe with machines and crane systems for iron and steel works, mines and ports. Together with two other machine factories, the company merged in 1910 to form Deutsche Maschinenfabrik AG, or Demag for short. Following the merger with the Mechanical Engineering Division of the United Steelmaking Division in 1926, the abbreviation "Demag" became the company name.

By the beginning of the 1970s, a global company with more than 22 subsidiaries and associated companies was created. The product range included machines and plants for conveying, compressor, compressed air and plastics technology, for metal extraction and forming as well as construction machinery.

The importance and long-term profit expectations in the product units represented by Demag prompted the Mannesmann Managing Board to take over more than a quarter of the share capital in 1972. Until 1983 Mannesmann acquired 100% of the shares.

The merger of SMS Schloemann-Siemag and Mannesmann Demag Metallurgie resulted in 1999 in a company which combined the strengths of both companies.