John James Hamilton, 1st Marquess of Abercorn (2 July 1756 – 27 January 1818) was an Anglo-Irish peer and politician.

Through the influence of John Buller, his wife's uncle, he was returned as a Tory Member of Parliament for East Looe in December, taking the seat vacated by William Graves.

Though deeply attached to Pitt, he possessed great independence of character and something of his uncle's stiff pride.

A staunch supporter of Warren Hastings, he spoke in 1788 against a bill to regulate (and thereby sanction) the slave trade, and in favour of its abolition.

[3] George W. E. Russell provided the following sketch of his aristocratic character:This admirable nobleman always went out shooting in his Blue Ribbon, and required his housemaids to wear white kid gloves when they made his bed.

Before he married his first cousin, Miss Cecil Hamilton, he induced the Crown to confer on her the titular rank of an Earl's daughter, that he might not marry beneath his position; and, when he discovered that she contemplated eloping, he sent a message begging her to take the family coach, as it ought never to be said that Lady Abercorn left her husband's roof in a hack chaise.

[10] They had one child: His marriage to Lady Cecil was not a success; they separated in 1798 and were divorced by Act of Parliament in April 1799.