He lived in Burnham Market in Norfolk Sir Mordaunt was a marshal of the vice admiralty court in Jamaica.

A keen agriculturalist, he wrote many letters and articles on the relative benefits of the mangel wurzel as a crop and is documented as the first person to introduce the plant, as well as sainfoin to the county and greatly improved the growth of potatoes and other vegetables.

On his death he left the hall-described by White as "a hand-some mansion, beautified with pleasure grounds and shrubberies, and situated near the church", to his son and heir Roger A portion of his early life was passed in the army, and he retained to his last moments that high sense of honour which a military-education so frequently instils.

He passed the last 50 years of his life in retirement at Burnham, devoting his time principally to the study and practice of agriculture.

"[5] Burnham was within visiting distance of Houghton Hall, then in the possession of Horace Walpole; the Martins took their former employee to admire the famous collection of paintings there.