General Sir Alexander Leith, KCB (1 December 1774 – 19 February 1859) was a Scottish officer in the British Army. He was born in Cobardie, Forgue, Aberdeenshire, Scotland, the son of Alexander Leith of Freefield & Glenkindie and Mary Elizabeth Gordon. He joined the British Army as an ensign in August 1792 and was made first a lieutenant and then captain in 1794. He was present with the 42nd Foot at the defence of Nieuwpoort, Flanders in 1794 and with the 31st Foot at the capture of St Lucia. He lost an eye at the Battle of Alkmaar in 1799.