He and his family were recusants — people who adhered to the Catholic faith after the English Reformation; nevertheless, Lord Petre was appointed to a number of official positions in the county of Essex.

A talented amateur musician, Lord Petre kept a full set of musical instruments (lute, five viols, virginals and organ) and was a patron of the composer William Byrd, a fellow Catholic who lived at nearby Stondon Massey.

In 1590, Lord Petre joined with Sir Thomas Mildmay in investigating the grievance of the mariners, gunners, fishermen, and other seafaring men within the county, who complained they were kept from their ordinary occupation by being constrained to attend at three hours’ warning for Navy service.

In 1600, Lord Petre installed his newly married son in Ingatestone Hall, to gain experience in the ‘government’ of a house, and the in-going inventory gives a vivid picture of it within a generation of the builder's death.

Art historian Roy Strong contends that these are in fact portraits of John's son and daughter-in-law, William Petre and Katherine, daughter of the Earl of Worcester.

His wife is equally in fashion; the cartwheel-topped skirt, the full upper sleeves and a variation of ruff open in front to show the neck, a delicate silver tiara and the splendid necklace of pearls, 1466 in all.