He was born in Monifieth, Forfarshire, Scotland, the son of Samuel Miller Low, a manufacturer of flax machinery, and educated at Madras College and the University of St Andrews.
In 1900 he spent three months in a malaria-ridden part of Italy and by avoiding mosquitos demonstrated that they were responsible for the transmission of the disease.
He spent 1901 in the West Indies, confirming Manson's discovery that filaria (a small worm) transmitted by mosquitos was the cause of elephantiasis.
In 1903 he was head of a team sent to Uganda to investigate the cause of "sleeping sickness", which failed to identify the true cause (Trypanasoma sp.)
On his return in 1903 he was appointed superintendent of the Albert Dock Seamen's Hospital (ADH) where the London School of Hygiene & Tropical Medicine was located.