Alexander MacDonell of Greenfield (1782 – 1835) was from a prominent family in Upper Canada. He was the sixth son of Alexander MacDonell of Greenfield and Janet Macdonell of Aberchalder (a sister of John Macdonell of Aberchalder). He was also the cousin and brother-in-law of Miles MacDonell.
Alexander worked as a fur trader and became a partner of the North West Company prior to become a political figure in Upper Canada. He served in the 8th Parliament of Upper Canada in the riding of Glengarry and in the 12th Parliament in the riding of Prescott.
He should not be confused with Alexander Macdonell who also served in the riding of Glengarry during several parliaments including the 6th Parliament in which the other Alexander Macdonnell succeeded Alexander MacDonell of Greenfield's brother, John MacDonell.
In 1822 Alexander became the Sheriff of the Ottawa District, a position he held until his death in 1835.