Alexander Macdonell of Greenfield (20 November 1782 – 23 February 1835) was a Canadian businessman and politician. He was the fourth son of Alexander Macdonell of Greenfield and Janet Macdonell of Aberchalder (a sister of John Macdonell of Aberchalder and Sir Hugh MacDonell of Aberchalder). He was also the cousin and brother-in-law of Miles MacDonell, the first governor of the Red River Colony. Another Alexander Macdonell also served in the riding of Glengarry during several parliaments, including the 6th Parliament; he succeeded Alexander MacDonell of Greenfield's brother, John MacDonell.