Born in Dublin, the son of a Huguenot refugee family. Married at least twice, to Elizabeth Wade (d. 1774) and to Anna Campbell (d. 1798). He also had a daughter from a previous relationship. She married Timothy Newmarsh, probably sometime around 1770. Trapaud's younger brother was General Cyrus Trapaud (1715-1801).
A military officer, Trapaud was Deputy Governor of Fort Augustus at the southern end of Loch Ness from sometime between 1746 and 1753 until his death in 1796.1 He had previously been Aid-de-Camp to Major-General Henry Ponsonby (1685-1745) at the battle of Fontenoy, when the general was killed by his side. He was afterwards Aid-de-Camp to General John Huske (ca. 1692-1761) at the battle of Culloden, when he was himself wounded.
According to a stone erected on the Kilcumein burial ground by his widow, Anna, Alexander Trapaud was "a brave Officer, Pious Christian and Faithful Friend, who served his king and Country for 63 years."
- 1The actual Governors of Fort George and Fort Augustus during Trapaud's tenure were Sir Charles Howard (1752-1765) and Studholme Hodgson (1765-1798), but as that office was largely sinecure, Trapaud,as Deputy Governor, was the de facto governor and principal authority of the fort for most of his time there.
Boswell had met Trapaud in Inverness in 1761, when he travelled with his father on the "circuit". They met again at Fort Augustus, where Trapaud was Deputy Governor, on August 29, 1773, during Boswell and Johnson's tour of Scotland. Trapaud invited them to stay the night at his house, which Boswell described as "a neat well-furnished house with prints, etc., a good supper (fricassee of moor-fowl, etc.); in short, with all the conveniencies of civilized life in the midst of rude mountains." Present were also Trapaud's wife, his daughter and her husband, Capt. Newmarsh. Boswell wrote of Trapaud that he "though near seventy, had excellent animal spirits, the conversation of a soldier and somewhat of a Frenchman, talking with importance of everything, however small."