John Macdonell or John MacDonell may refer to:
Lieutenant Colonel John Macdonell of Greenfield (19 April 1785 – 14 October 1812) was an aide-de-camp to British Major General Sir Isaac Brock during the War of 1812, dying in the Battle of Queenston Heights.
He was born on 19 April 1785 in Scotland near Aberchalder and came to Canada when he was seven years old. There he studied to become a lawyer and was called to the bar at the age of 23, opening his own law office. An interest in politics earned him a seat on the legislature and an appointment as attorney-general.
He also became a lieutenant colonel in the York Militia and, at the outbreak of the War of 1812, became secretary and provincial aide-de-camp to General Isaac Brock. On 13 October 1812, during the Battle of Queenston Heights, Brock was struck and killed by an American musket ball. Despite being a lawyer by trade with little military experience, Lieutenant-Colonel Macdonell, along with Captain John Williams of the 49th Foot, led a second attempt to retake the Redan, one that was very nearly successful.
Sir John Macdonell K.C.B. (1 August 1846 – 17 March 1921) was a British jurist. He was King's Remembrancer (1912–1920) and a Knight Commander in the Order of the Bath.Shaw of Dunfermline gives a prefatory biography in Historical Trials.
Colonel John MacDonell (1728-1810) of Scotus was a Spanish officer and a Highland gentleman who emigrated to the Province of New York in 1773. He was a Loyalist in the American Revolutionary War and emigrated to Upper Canada after the war.
He was born 1728 into the clan MacDonell of Glengarry, the son of John of Crowlin. As a boy he was sent to the Scots College in Rome. He obtained a commission in one of the Irish regiments in the service of Spain. He saw some action in Italy and was promoted from cadet to lieutenant before volunteering. In 1746 he was part of the invasion force which the French government assembled, Irish Brigade (French), to assist the Jacobite rebels in Britain. In 1773 he emigrated with others in his clan to Caughnawaga in the Mohawk valley of the Province of New York at the invitation of Sir William Johnson.
After the war he settled in Upper Canada near St. Andrew's where he died on April 15, 1810.
His son Miles Macdonell was the first governor of what is now Manitoba, another son John McDonell (Le Prêtre) become a political figure in Upper Canada.