 He was educated at Totnes grammar school, and at age 14 was placed in the counting-house of Messrs. Jackson & Co., a firm of Russia merchants in London.Venning went to St. Petersburg in 1793, and made as successful career there as a merchant.His interest in the condition of Russian prisons was aroused by his brother Walter Venning; and in 1819, on the foundation of the St. Petersburg Society for the Improvement of Prisons, he became its treasurer.