James Ernest Cox was the eldest son of Ada Mary Cox and Edward Cox of Cardean and Drumkilbo, Meigle. Educated at a preparatory school and at Uppingham, he then studied at Pembroke College, Cambridge, where he graduated B.A.
In 1899 he joined the firm of Messrs Cox Brothers. He became a leading authority in jute and in 1920, when Jute Industries Ltd acquired companies in the city, including Cox Brothers Ltd, he was chairman of the firm. From 1920 until 1948 he was a chairman of Jute Industries Ltd and its subsidiary companies and was a prominent figure in the business and commercial world. Following the death of his father In 1913 he joined the Board of the First, Second and Third Scottish-American Trust Company and the Northern American Trust Company. Later he became chairman of the companies and held these positions, along with that of chairman of the Camperdown Trust Company Ltd, until his resignation in 1947. He was a member of the local board of the Northern Assurance Company Ltd, and an extra-ordinary director of the Scottish Widows' Fund and Life Assurance Society. In 1919 he became president of the Chamber of Commerce and for many years he was a prominent member of the Association of Jute Spinners and Manufacturers.
In 1906 he became a member of the Council of University College, Dundee. Later he was appointed convener of the finance committee and in 1926 was appointed chairman of the council. In 1931 his services to the university were recognised when he received the honorary degree of LL.D. in 1931. He resigned from the chairmanship in 1939, and three years later was elected president of the College, a position he held for until 1946.
In 1934 he was appointed by the Scottish Secretary to the Committee on Scottish Health Services, established to review the entire national health policy and organisation in Scotland. JE Cox served for six years as a director of Dundee Royal Infirmary and wad also vice-president of the Royal Victoria Hospital. He was a General Commissioner of Income Tax for the Division of Dundee.
Dr Cox lived at Lyndhurst, Lochee prior to purchasing Methven Castle in 1922. The estate, of almost 1000 acres, comprised the mansion-house; policies and woodland; the home farm; and the farms of Easter Busby, Loanleven, and Easter, Middle and Wester Powside. He had an interest in agriculture, particularly pig breeding and won prizes at many shows, including several at the Royal Highland Show. He was also president of Methven Curling Club. While resident in Dundee Dr Cox was identified with St Margaret's Episcopal Church but after the purchase of Methven, he was prominently associated with St Ninian's Cathedral, Perth, being treasurer of the Diocese of Brechin for 25 years.
He married Agnes Jane Tod in 1904. His wife, three sons, Commander David E. Cox, Michael George Cox and Douglas Hunter Cox and a daughter, Margot Cox, survived him. His first born son, Edward James Cox, had been killed in a motorcycle accident in 1925. A daughter Kathleen Mary Cox was born and died in 1911.