The firm provided planning, design and construction management for water and natural resources projects around the world.

As of May 2015, MWH Global had a global staff of approximately 7,000 employees[2] including builders, engineers, architects, geologists, operators, project managers, business consultants, scientists, technologists, and regulatory experts.

[5] JMM was founded in Pasadena, California, in 1945 by James M. Montgomery[6] following his work on the design (1936) and commencement (1941) of the 100-million gallon per day F. E. Weymouth Memorial Water Softening and Filtration Plant at La Verne, California for the Metropolitan Water District of Southern California while with the firm Hoover and Montgomery.

[8] In 2001, Montgomery Watson merged with Harza Engineering Company, of Chicago, Illinois, best known for its work in the energy and environmental sectors and hydroelectric power development[9] including the El Cajón Dam in Honduras (officially known as Central Hidroeléctrica Francisco Morazán), and operated under the new name of Montgomery Watson Harza.

[8] In 2010, MWH acquired Biwater Services Ltd., a water construction and engineering firm.