Sir John Fortescue was the eldest son of Sir Adrian Fortescue, whom had be executed by King Henry VIII in 1539, probably due to Sir Adrian's closeness to Anne Boleyn. She was his second cousin and had fallen from grace and been beheaded three years earlier. John was only eight at the time of his father's death and although the family estates were confiscated in 1539, they were restored to the family in 1551. John's mother had remarried and his step-father was made Comptroller of the Royal Household on the accession of Queen Mary in 1558. John was appointed as the supervisor of Princess Elizabeth's studies. He was a renowned Greek and Latin Scolar and would later in life be described by Lloyd in State Worthies, 1670, as 'A great master of Greek and Latin'.
On the accession of Queen Elizabeth I, in 1558, he was appointed Keeper of the Great Wardrobe. He became M.P. for Wallingford in 1572 and Chancellor of the Exchequer on the death of Sir Walter Mildmay in 1589. This extremely lucrative appointment enabled him to build a magnificent house, Salden, at Mursley in Buckinghamshire, a single wing of which survives, having become a farmhouse in the 18th century. A further appointment in 1601, as Chancellor to the Duchy of Lancaster, increased Sir John's already large income. His wealth allowed him to keep a retinue of some sixty servants. Although he, with Sir Walter Raleigh and others, attempted to curtail the number of Scots appointed to offices of state, after the succession of James I, he was on good terms with the new King, and entertained him on a number of occasions. He died at his house in Westminster in 1607. He was buried in the church at Mursley, where a tomb was raised in his memory.