He travelled around the British colonies, examining agriculture and livestock husbandry, and wrote numerous books and contributed several entries related to farming for the 11th edition of Encyclopaedia Britannica.
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.
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.
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.
He retired in 1922 but continued to hold advisory positions and represented the Scottish Board of Agriculture in the 1923 World Dairy Congress in Washington D. C.[10] He died at Mid Park House, Kincardine-on-Forth on 17 January 1939 aged 85.