John Barnewall, 3rd Baron Trimleston (d. 25 July 1538), was an Irish landowner and politician. He was the eldest son of Christopher Barnewall, 2nd Baron Trimlestown and Elizabeth Plunket, daughter of Sir Thomas Plunket of Rathmore, Lord Chief Justice of the King's Bench in Ireland . He succeeded his father as 3rd Baron about 1513.
His ancestors came over originally with Henry II. and received large grants of land in the County of Cork. On the first favourable opportunity the old proprietors, the O'Sullivans, rose and murdered the whole family save one young man, who was absent studying law in England. He ultimately returned and settled at Drimnagh, near Dublin The subject of our sketch rose to high office in Ireland under Henry VIII. and received grants of land near Dunleer. He was unusual among the Irish nobility of the time both in his professional legal skills and his willingness to take judicial office ( O'Flanagan[1] suggests he wished to emulate his grandfather Chief Justice Plunket. ) He was made Attorney General for Ireland in 1504, Solicitor General for Ireland and King's Serjeant shortly after, a justice of the Irish Court of KIng's Bench in 1514, Deputy Treasurer and then Lord Treasurer of Ireland in 1524 and Lord Chancellor of Ireland in 1534.[2] O'Flanagan praises him as an expert on finance as well as law, but adds somewhat cynically that his expertise extended to looking after his own interests[3], noting the substantial grant of land at Dunleer in particular. In 1536, with Lord-Treasurer Brabazon, he made an incursion into Offaly, and drove back the O'Conor, who was then ravaging the Anglo-Irish settlements. The next year, commissioned by the Privy Council, he treated successfully with the O'Neill. He died 25th July, 1538. He was four times married.[4] Only the names of his first and second wives, Janet Bellew and Margaret Fitzlyons, are known for certain. Despite his numerous marriages only two children are recorded:
Patrick Barnewall (Solicitor General) and Master of the Rolls in Ireland, was his nephew.