[3][6] Through his aunt Elizabeth de Ponthieu, he was a first cousin of the banker Charles Wilkes.
A member of Bruce, de Ponthieu, Bazett & Co. until his death, he was shareholder and writer for the East India Company in Bombay in 1783, he was a factor in 1790 before becoming secretary and accountant to the Military Board in 1795.
[3] De Ponthieu, like his business partners Patrick Craufurd Bruce, George Simson, and Henry Fawcett of Scaleby Castle, sought to purchase a seat in Parliament and was returned, briefly, on two different occasions.
[3] De Ponthieu, who never married, lived at 43 Portland Place, Middlesex, and acquired a residence at Esher.
His 1803 will, which was contested by his business partners, left £20,000 to his unmarried sister Anne,[3] who died in 1823.