- For the Canadian parliamentarian see James Macdonnell (Canadian politician)
In 1794, he was a lieutenant in the 78th (Highlanders) Regiment of Foot; in 1795, he was Captain in the 17th Dragoons. He joined the 19th Foot in 1796; he was major in the 78th Foot, and was awarded the Army Gold Medal for Maida in 1806. He joined the Coldstream Guards in 1811 as a Lieutenant Colonel, and served in the Peninsular War. 
He is most famous for his command of the light troops defending Hougoumont at the battle of Waterloo, 1815, where he fought with great distinction, including leading the vital closing of the gates, with his sergeant, James Graham. He was wounded slightly in the battle. 
He was awarded Order of the Bath, Knight's Cross of Maria Theresa, and Royal Guelphic Order for his service at Waterloo.
He was appointed Grand Cross in the Order of the Bath in 1855, Colonel-in-Chief of the 71st (Highland) Light Infantry.
- Burke's landed gentry of Great Britain, Editor Peter Beauclerk Dewar, Burke's Peerage, 2001, ISBN 978-0-9711966-0-5
- "Armed Forces: Units: British Infantry: The Coldstream Guards". British Empire. Retrieved 2010-08-11.
- Ian R Gumm. "The Waterloo Campaign 1815 - Aftermath". Battlefield-tour.com. Retrieved 2010-08-11.
- Julian Paget & Derek Saunders (1992); Hougoumont: The Key to Victory at Waterloo; Pen and Sword Books (paperback 2001) ISBN 0-85052-716-3