Matthias Barnewall, 10th Baron Trimlestown (1670 – 8 September 1692) was an Irish Jacobite peer and soldier.
He was the son of Robert Barnewall, 9th Baron Trimlestown and Margaret Dungan, and was educated in France.
In June 1689 he succeeded to his father's title, and was one of the Roman Catholic peers who attended the Irish House of Lords in the Patriot Parliament of 1689.
He was appointed a Lieutenant in the Duke of Berwick's 1st Horse Guards in French service, and died at the age of 22 in a cavalry charge at the Battle of Ortheuville (Roumont) on 8 September 1692.
[2] He never married and was succeeded in his title by his younger brother, John, who petitioned successfully to recover his family's confiscated Irish estates from Henry Sydney, 1st Earl of Romney.