Wallace was born on 24 June 1853 in the ancestral family home, Wallace Hall in
Glencairn,
Dumfriesshire, the second son of Susan Reid and her husband, Samuel Wallace, a gentleman farmer. He was educated at
Tynron Parish School and then Hutton Hall Academy near Bankend. He then studied at the
University of Edinburgh graduating with an MA around 1872. He then spent ten years farming his father's estates along with his brother Samuel Williamson Wallace (1855–1932) who became director of agriculture for the state of Victoria in Australia in 1902. From 1882 to 1885, he began to teach at the
Royal Agricultural College in
Cirencester and served as a Professor of Agriculture. In 1885, he returned to Edinburgh as Professor of Agriculture and Rural Economy. In 1886, he was elected a Fellow of the
Royal Society of Edinburgh proposed by
Robert Gray, John Wilson,
Peter Guthrie Tait and
Henry Alleyne Nicholson. He worked towards the establishment of BSc degrees in agriculture and in helped found the
Edinburgh and East of Scotland College of Agriculture in 1906. From 1915 to 1917, he corresponded with
President Woodrow Wilson of the
United States on the ill-treatment of prisoners-of-war by Germany and sought American intervention. Wallace was Garton Lecturer on Colonial and Indian Agriculture (1900-1922) which helped spread his reputation across the colonies. Wallace travelled widely, to Italy and India in 1887, the latter resulting in a book
India in 1887 in which he examined livestock farming and agriculture in India. Wallace travelled to India in an unofficial capacity, with a special interest in livestock. He took numerous photographs and several notes were published in scholarly societies. Communicating with
Thomas Henry Huxley, he speculated on the skin colours of Indian cattle, commenting that they were predominantly dark skinned and suggested that they may have been selected for the same underlying but unexplained mechanism leading to darker human skin colour in the tropics. He travelled to the United States thrice between 1890 and 1898 with trips to Egypt (1891), Greece (1892) and South Africa (1895) in the same period. He corresponded extensively with
Eleanor Ormerod and edited a biography of her published in 1904. In 1900, he was living at 5 Mansfield Place in
Edinburgh's New Town. From 1910 to 1923, he was living at 21 East Claremont Street. He died at Mid Park House, Kincardine-on-Forth on 17 January 1939 aged 85. ==Publications==