Alexander MacDonnell may refer to:
- Sir Alexander Macdonnell (died 1634), of the Macdonnell baronets of Maye
- Sir Alexander Macdonnell, 1st Baronet (1794–1875), of the Macdonnell baronets of Kilsharvan
- Alexander MacDonnell, 3rd Earl of Antrim (1615–1699)
- Alastair Ruadh MacDonnell (c. 1725–1761), also called Alexander
- Alexander Macdonell (bishop of Kingston) (1762–1840), first Roman Catholic bishop of Kingston, Upper Canada