His father was John Frazer, minister of the Associate Church at Auchtermuchty, in Fife, Scotland. His mother was Margaret Erskine. He became minister of the Associate Church at Saltcoats in Ayrshire, in 1796, but within months inherited an estate through his mother, at Lassodie, Beath, in the Fife coalfield.
Dewar graduated Doctor of Medicine
At this point Dewar left the ministry. Dewar retrained as a doctor at Edinburgh University gaining an Doctor of Medicine in 1804. He then began a new life as an army surgeon, with the 30th Regiment of Foot.
In Egypt under Ralph Abercromby, he underwent some formative experiences, writing later on dysentery and ophthalmia.
He also came under the influence of French physicians (Savaresi, Larrey, and Desgenettes). at Edinburgh in 1804, with a dissertation De ophthalmia Aegypti. He was a Manchester Infirmary staff physician, from 1804 to 1808, a common step for Edinburgh medical graduates because of the breadth of professional experience there.
He may have dropped medical practice, and become a writer He was elected a Fellow of the Royal Society of Edinburgh in 1816.
His proposers were Sir David Brewster, Andrew Coventry, and John Barclay.
In his later life he lived at 37 Nicolson Street in Edinburgh"s South Side. The house stood immediately opposite Surgeons" Hall but was demolished in the late 19th century to make way for a small department store. He died on 18 January 1823 and was buried in Street Cuthbert"s Churchyard on the following day.
They had six children.
Dewar died on 19th January 1823 and is buried with his family in the south-west corner of the north extension to Street Cuthberts Churchyard in Edinburgh.
He became a member of the Manchester Literary and Philosophical Society in 1806. He then returned to Edinburgh, becoming a member of the Royal College of Physicians there and lecturer at the Medical Institution.
