[1] John was son of Joseph Walsh, Secretary to the Governor of Fort St. George and cousin to Nevil Maskelyne, the Astronomer Royal, and his sister Margaret, the wife of Lord Clive.
He entered the English East India Company at the age of fifteen and eventually became Clive's private secretary.
Upon his return to England in 1759, his fortune was estimated at £147,000, and he quickly sought to purchase the necessary trappings of aristocratic power in eighteenth century Britain: land and political influence.
In 1778 the major of the Worcestershire Militia died soon after the regiment had been embodied for home defence duties during the American War of Independence.
[6][7] He was elected a Fellow of the Royal Society in 1770 and awarded their Copley Medal in 1773 for a paper on the electrical properties of torpedo fish.