Born in 1576[1] in Cornwall, the eldest son of Edward Borlase of London, a mercer, and Suzannah Isham.
[3] Borlase served as a soldier in the Low Countries, taking part in the expedition to the Palatinate in 1620 under Sir Horace Vere to defend the Protestant cause.
In 1633, he was appointed Master of the Ordnance in Ireland, jointly with Sir Thomas Lucas, a post he held until his death.
[4] Following the recall to England of Lord Deputy of Ireland, Thomas Wentworth, 1st Earl of Strafford, Borlase and Sir William Parsons were appointed joint Lord Justices of Ireland in February 1641.
As Wentworth's successors were either ill (Christopher Wandesford) or absent (Robert Sidney, 2nd Earl of Leicester) the two men were the virtual rulers of Ireland until their dismissal in 1644 when the Marquis of Ormonde took over as Lord Lieutenant.