Samuel James Donaldson (March 12, 1856 – March 14, 1926) was a farmer, rancher, police officer and political figure in Saskatchewan, Canada. He represented Prince Albert County and then Shellbrook in the Legislative Assembly of Saskatchewan from 1905 to 1915 as a Provincial Rights-Conservative MLA and Prince Albert in the Canadian House of Commons from 1915 to 1917 as a Conservative MP.
He was born in Appleton, Canada West, the son of Samuel Donaldson. After completing his education, he worked as a clerk in a furniture store in Ottawa. In 1876, joined the North-West Mounted Police and travelled west to Pelly, Saskatchewan. Donaldson was a member of the force from 1876 to 1882, serving in Battleford, Prince Albert and Qu'Appelle. He served as a captain in the Prince Albert Scouts during the North-West Rebellion. After he retired from the Mounted Police, he entered the livery business. In 1882, he married Jessie Paterson.