Sir Donald Mann (March 23, 1853 - November 10, 1934) was a Canadian railway contractor and entrepreneur.

Born at Acton, Ontario, Mann studied as a Methodist minister but worked in lumber camps in Ontario and Michigan before moving to Winnipeg, Manitoba. During the 1880s he worked as a contractor building sections of the Canadian Pacific Railway across the prairies and through the Rocky Mountains.

Partnering with William Mackenzie, Mann built railway lines in western Canada, Maine, Brazil, and China. In 1895, together with Mackenzie he began the process of purchasing and/or building the lines in western Canada which would later become the Canadian Northern Railway (CNoR), a system which would stretch from Vancouver Island to Cape Breton Island and form Canada's second transcontinental railway system.

Both Mann and Mackenzie were knighted in 1911 for their efforts in the Canadian railway industry, however personal and company financial difficulties eventually resulted in the bankruptcy of the CNoR and it was nationalized by the federal government on September 6, 1918.

Mann turned to mining and died in Toronto, Ontario.