He was the eldest son of Sackville Fox of East Horsley, Surrey, and his wife Ann Holloway.
Mackreth bought Fox-Lane's Surrey estate very shortly after James came of age in 1777 and resold it for a handsome profit.
His suit was successful, and he was awarded the purchase money of the Surrey estate with interest and costs, totaling about £20,000.
Frances, the Dowager Viscountess of Irvine, was one of his Yorkshire neighbours, and in the 1796 election, returned him for one of the seats she controlled at Horsham.
[5] Through his son William he was a grandfather of Augustus Pitt Rivers,[4] a prominent English ethnologist, and archaeologist.