Alexander McDonnell was an Irish locomotive engineer and civil engineer. He was born in Dublin on 18 December 1829 and died in Holyhead on 14 December 1904. He was educated at Trinity College, Dublin, where he graduated with an honours BA in mathematics (1851). He brought order and standardisation to the workshops and locomotive designs of the Great Southern and Western Railway of Ireland, and was later employed to do the same for the North Eastern Railway in England, although resistance to his changes meant little progress was made before he left.