Sir Patrick Barnewall or Barnwall (died 1622), was the eldest son of Sir Christopher Barnewall of Turvey, Grace Dieu Abbey, and Fieldston. Christopher in turn was the son of the elder Sir Patrick Barnewall, who in 1534 was made Serjeant-at-law (Ireland) and Solicitor-General for Ireland, and in 1550 became Master of the Rolls in Ireland. Patrick's mother was Marion Sherle, daughter of Richard Sherle of County Meath: after his father 's death she remarried the prominent judge Sir Lucas Dillon.
Sir Christopher was Sheriff of County Dublin in 1560, and is described by Raphael Holinshed, his son in law, as ‘the lanthorn (i.e. lantern) and light as well of his house’ as of that part of Ireland where he dwelt; who being sufficiently furnished as well with the knowledge of the Latin tongue, as of the common laws of England, was zealously bent to the reformation of his country.’ Sir Patrick Barnewall ‘was the first gentleman's son of quality that was ever put out of Ireland to be brought up in learning beyond the seas’. He succeeded his father in his estates in 1575. He married firstly Mary St. Lawrence, daughter of Lord Howth, but the marriage was annulled in 1579 and in 1582 he remarried Mary, daughter of Sir Nicholas Bagenal, knight mareschal of Ireland, with whom he had a son and four daughters. She died in 1609. Her sister Mabel, celebrated for her elopement with Hugh O'Neill, 2nd Earl of Tyrone in 1591, lived with them at Turvey, for a time, and it was from Turvey, with the connivance of Sir William Warren, that Mabel fled to Warren's home at Drumcondra, where her marriage to O'Neill took place. After the death of Mary's eldest brother Henry Bagenal at the Battle of the Yellow Ford in 1598, Patrick was appointed guardian of his children.