Barnewall, John (1470–1538), 3rd Baron Trimleston , administrator, was son of Christopher Barnewall, 2nd baron, and his first wife, Elizabeth Plunket of Rathmore, Co. Meath. Christopher (pardoned in 1488 for his part in Lambert Simnel's (qv) rebellion) died a.June 1513. John, who appears as a pleader at the bar in 1504 and (later in the same year) king's attorney, king's solicitor, serjeant, and judge, was knighted a.2 January 1514, when he was made second justice of king's bench. Having helped to negotiate a truce between the earl Desmond (qv) and Piers Butler (qv) (1520), he became a privy counsellor in late 1521 and under-treasurer in 1524, perhaps to balance Butler's treasurership. He was chancellor from 16 August 1534 till death; may have acted as governor pending the arrival of Sir William Skeffington (qv) in late 1534; and received large grants of land in Dunleer, Co. Louth. As he was a FitzGerald protégé, his allegiance at the start of the rebellion of Silken Thomas (qv), was suspect, but he accompanied Skeffington in the rebels’ defeat (1535), and Lord Leonard Grey (qv) in expeditions against the earl of Desmond (qv) and the O'Briens (1536) and O'Connor Faly (1537); he also negotiated successfully with O'Neill (qv) (1537) near Dundalk, Co. Louth. He died 25 July 1538.
Barnewall married first Janet (Genet) Bellew of Bellewstown, Co. Meath, with whom he had one son, Patrick (later 4th baron); and secondly Margaret FitzLeons of Newland, with whom he had four sons and two daughters. The dates of his marriages, and the names of two later wives, are unrecorded.