William Mildmay (1705-1771) was born in Surat, India, to Sarah Wilcox and William Mildmay, a civil servant in the East India Company. Orphaned by his sixth birthday, Mildmay and his sister Mary were raised by guardians Edmund and Elizabeth Waterson. At the age of eighteen, Mildmay entered school to become a lawyer. After entering the bar, Mildmay worked in a minor capacity for British government officials, which eventually earned him a place with William Shirley (1694-1771) on the Anglo-French Commission in Paris from 1750-1755. The purpose of the commission was to settle the final disputed sections of the Treaty of Aix-la-Chapelle, signed in 1748, to end the War of Austrian Succession. Issues at hand included the boundaries of Nova Scotia; the right to the islands of St. Lucia, Tobago, St. Vincent, and Dominica; and the accounts of prizes taken at sea after the signing of the preliminary articles of peace. Mildmay was separately commissioned to effect the exchange of prisoners. In May 1752, Ruvigny de Cosne (1715-1775), secretary of the British embassy in Paris, succeeded Shirley. Negotiations dragged on for several years, and the failure of the commission to conclude a lasting treaty with France influenced the outbreak of the Seven Years' War in 1756.
After the commission finished its mission in 1755, Mildmay returned to England, where he wrote an official report on the commission. Mildmay wrote several books on French society based on his time living in France. During the Seven Years' War, Mildmay served as a captain in the militia, and later as sheriff of Essex. After the death of several relatives, Mildmay inherited the estates of Moulsham and Chelmsford. He married his cousin Anne, heiress of the estate of Shawford, Hampshire. He was created a baronet in 1765, and died childless in 1771.