Alexander MacDonnell, 3rd Earl of Antrim

Alexander MacDonnell, 3rd Earl of Antrim (1615 – 10 December 1699) was a Roman Catholic peer and military commander in Ireland. He was the son of Randal MacDonnell, 1st Earl of Antrim and his wife, Alice O'Neill (Alice was the daughter of Hugh Ó Neill, 2nd Earl of Tyrone).

After coming of age, MacDonnell spend three years abroad in Europe before returning to Ireland just before the outbreak of the Irish Rebellion of 1641. MacDonnell was commander of a regiment of Irish against Cromwell in 1641, and soon took his place among the Irish leadership. Unlike his brother, Randal, he urged a conciliatory approach to the English under Oliver Cromwell. He remained in command of a regiment until the Confederation surrendered to Cromwell in 1652. His lands were confiscated and distributed amongst Cromwellian soldiers. By 1656, MacDonnell was living in England, and at Restoration was restored to his lands.

In 1680, MacDonnell was appointed custos rotulorum for Antrim, and he succeeded to the title of Earl of Antrim on 3 February 1682 on the death of his brother. He was invested as a Privy Counsellor and Lord-Lieutenant of Antrim shortly after the accession of King James II, as the King followed a policy of replacing Protestants with Catholics across Ireland. At the outbreak of the Glorious Revolution, MacDonnell adhered to James and presided over the unsuccessful siege of Derry. On James's defeat, MacDonnell's lands and titles were, again, declared forfeit. In 1697 he was restored to his title.

He married, firstly, Lady Elizabeth Annesley, daughter of Arthur Annesley, 1st Earl of Anglesey. She died childless in 1669. He married, secondly, Helena Burke, daughter of Sir John Burke of Derrymaclachtney, after 1672. They had one son, Randal, and one daughter, Mary.