Charles Alexander Magrath conducted foundation surveys of the Northwest Territories from 1878 until 1885. He joined Sir Alexander Tilloch Galt and Elliot Torrance Galt in their western industrial enterprises as a surveyor, later becoming Elliott's assistant and Land Commissioner of the North Western Coal and Navigation Company. He was also the first mayor of Lethbridge, Alberta, which has a major street (Mayor Magrath Drive) named after him.
Magrath was a member of the Northwest Territories Legislature from 1891–1898). He was appointed as a cabinet minister in the Frederick Haultain administration in 1897. In the 1891 and 1894 general elections and an 1897 by-election, he represented Lethbridge and was acclaimed.
Magrath ran as a Member of Parliament representing the Medicine Hat constituency (1908–1911). He was fuel Controller during the Great War and chairman of Ontario Hydro and the Canadian section of the International Joint Commission. He also served on the Newfoundland Royal Commission of 1933.
He married Margaret Holmes White Mair in 1887. After giving birth to a son, Charles Bolton, in 1888, she died in June 1892 of complications following the birth of a daughter. In 1899, he married Mabel Lillian Galt, a daughter of Sir Alexander and half-sister of Elliot Galt. Two daughters were born of this union: Amy and Laura.
Magrath has been called "The Father of Irrigation in Southern Alberta". However, during his lifetime he was quick to acknowledge the contributions of Charles Ora Card, the LDS Church, and Elliot Galt to the development of irrigation in the Lethbridge region. The community of Magrath, Alberta is named in his honour.