Born the eldest son of John Hamilton-Leslie, 9th Earl of Rothes and Lady Jean Hay, daughter of John Hay, 2nd Marquess of Tweeddale, Leslie was commissioned into the 9th Regiment of Dragoons in 1715.

[1] He became Commanding Officer of the 21st Regiment of Foot in 1721 and inherited his father's title the following year.

[1] In 1747, under the Heritable Jurisdictions Act, he sold the office of Sheriff of Fife, which had been a hereditary right of the earldom since 1540.

[3] In 1741 he married Hannah Howard, daughter of Matthew Cole of Thorpe, Norfolk and his wife Brittania Cole; they went on to have two sons and two daughters, including John Leslie, 11th Earl of Rothes and Jane Elizabeth Leslie, 12th Countess of Rothes, who succeeded to her brother's title, defeating the rival claim of her uncle Andrew.

[1] Mary, the youngest daughter, married William Colyear, 3rd Earl of Portmore.