During his studies, he was influenced greatly by Alexander Bain and was a one-time associate of Edwin Chadwick, another major public health figure.

Helen pursued an active political career including supporting women's emancipation and the right to vote,[4] and also served on many health boards and committees.

[2] While Mackenzie was quickly becoming a major player in his field, complaints from MPs on the state of medical provision in the highlands prompted even more change.

[1] The following year, he and his wife Helen collaborated on the 1903 Royal Commission for Scotland report on the health of school children in Edinburgh.

This report led to the introduction of a school meals service and medical inspection after much debate in Parliament,[2] and recommendations were included in the 1908 Education (Scotland) Act.

[4] Mackenzie's career continued to be punctuated by fierce arguments and strong defense of his own medical findings and beliefs.

In 1902, he vigorously disagreed with the Scottish medical establishment on the infectivity of tuberculosis at a meeting in Edinburgh of the Medico-Chirurgical Society.

[2] While he sat on the board he gave evidence for the care of elderly and feeble minded (1908), strongly opposed the eugenics movement and the poor laws (1909) and called for a preventative health service run by the local authority instead.

His treatment plan was designed to overcome the great difficulties associated with providing medical care for a small population scattered over a wide area where transport is usually difficult.

His colleagues regarded him “with awe, as a radical philosopher who saw medicine not as a palliative nor a means of private gain, but as an instrument of social development”.

His publications on behalf of the sick pauper, the TB victim, the mother, the school child, and the inner city tenant all embodied his idea of social advancement through positive intervention.

Sir Leslie William Mackenzie died on 28 February 1935 in Edinburgh, after enduring a long illness and was cremated on 2 March.