Sir Nicholas Barnewall (died after 1465) was an Irish judge and landowner of the fifteenth century who held office as Lord Chief Justice of Ireland.
He married Ismay, daughter and co-heiress of Sir Robert Serjeant of Castleknock, County Dublin: they had at least two sons, Christopher and Edmund.
There was a bitter dispute over the family inheritance between the two sisters and their respective husbands, from which the Barnewalls emerged the winners, acquiring far more than the half share of the estate to which Ismay was entitled by law.
Ismay outlived her husband, and remarried the prominent Yorkist nobleman Sir Robert Bold, 1st and last Baron Ratoath, who died in 1479.
Catherine Bold, Lord Ratoath's daughter and heiress by his previous marriage, married Nicholas and Ismay's younger son Edmund Barnewall: they settled at Dunbrow in County Dublin, where their descendants remained for several generations.