Sullivan was born on 15 June 1788, the son of John Sullivan (1749 –1839), of Richings Park, Iver, Buckinghamshire, the second son of Benjamin Sulivan of Cork (1720–67), Clerk of the Crown for Waterford and Cork [Kinsman of Laurence Sulivan, Chairman and Director of the East India Company] and Lady Henrietta Hobart, daughter of George, 3rd Earl of Buckinghamshire and sister of Robert, Lord Hobart, one of Pitt's Secretaries of State.

In 1819, he set out to explore the Nilgiris after obtaining an order from the British East India Company charging him with investigating the "origin of the fabulous tales that are circulated concerning the Blue Mountains to verify their authenticity and to send a report to the authorities".

After touring the area in 1819, John Sullivan began a personal campaign to persuade the government of Madras that the location's "unusually temperate and healthy" climate made it ideal as a "resort of invalids," primarily soldiers.

Their reports persuaded the Board that "we fully anticipate very great advantages from a resort to these Hills," and it recommended that fifty invalid soldiers be sent there to test the region's salubrity.

His wife, who had the distinction of being the first European woman in the Nilgiris, moved into the house in 1823 along with his infant son and others who made Ooty their abode including Sir Thomas Munro, the governor of Madras, who stayed at Ootacamund.

Sullivan's dream of making it a sanatorium for British troops had been fulfilled, but the Government's action meant that Ooty would no longer be in his control but in that of his rival Major William Kelso.

The first house which Sullivan built at the village Hosatti, near Kotagiri, is currently the only memorial left in the Nilgiris save for the font donated in his name to St. Stephen's Church by Col. & Mrs. Gilhlan in 1872.

Under Sullivan's influence local roads, a market, and such civic buildings as a courthouse, a hospital, a post office, a bank and a jail arose.

[3] A second son, Augustus William Sullivan, also served in the Madras Civil Service, born in 1813; he died in 1858 and is buried at St. John's Cemetery in Tellicherry.