[3][4] Mackenzie had become part of the suffrage movement as early as 1891, under the influence of Elizabeth Clarke Wolstenholme Elmy in WEU in Newton Stewart, Galloway.
[5] Mackenzie went on to be one of the founders of the Edinburgh Women Citizens' Association in 1918, alongside Mona Chalmers Watson,[5] and was described as the 'most active executive committee members' and over these years she worked for women's emancipation alongside Elsie Inglis, Flora Stevenson, Louisa Stevenson, Mary Burton, and Jessie Methven.
McKenzie and her husband argued that teachers should be trained in health issues and many of their recommendations were adopted into the 1908 Education (Scotland) Act.
[7] After her husband’s knighthood, known as Lady Leslie Mackenzie, she became one of the founding committee members on the University of Edinburgh's School of Social Study and Training, where she taught a course on Local Government from 1918 until at least 1932.
[8] In addition, she had a long involvement with the Edinburgh College of Domestic Science (which later was absorbed into the Queen Margaret University), chairing it from 1943 - 1945.