He was born on 1 October 1748 the son of John Dewar and Elizabeth Jean Forrest.
[2] In 1782 Dewar was one of the founding members of the Harveian Society of Edinburgh and served as President in 1790 and 1814.
[4] In 1786 he is listed as a Manager of the Edinburgh Dispensary alongside Dr Benjamin Bell, James Hunter and Thomas Elder.
In 1801 he is recorded as living at 9 Hunter Square, off the Royal Mile in Edinburgh's Old Town.
[6] In the same year he appears as an expert witness in the court case Rollo v Irving.