Alexander Johnson (August 1, 1830 – February 11, 1912) was an Irish mathematician and academic.

[1] Born in Ireland, Johnson was educated at Trinity College, Dublin (TCD) where he was a scholar in 1852 and received his B.A.

In 1857, he had emigrated to Canada and was appointed a professor of mathematics and natural philosophy at McGill University.

[2] He received an honorary DCL from the University of Bishop's College, Lennoxville in 1882.

He was an original member of the Royal Society of Canada and was made a fellow.