Roderick Macdonald was born c. 1840 in Scotland, the son of a crofter. He received his education first at Free Church Normal School, then at Glasgow University. He taught at Free Church School, Lonmore before studying medicine. In 1867 he became a Licentiate of both the Royal College of Physicians and the Royal College of Surgeons, Edinburgh. He also became a member of the Inner Temple, one of the four Inns of Court a barrister or judge must be part of. He practiced medicine in the East End of London, and worked with the police as a divisional surgeon for the Isle of Dogs.
He was a member of the Crofter's Party, and in 1885 was elected a Member of Parliament for Ross and Cromarty, a seat that he held until he stepped down in 1892. In 1887 he was elected coroner for part of East Middlesex. In this capacity he presided over the November 12th, 1888 inquest into the murder of Jack the Ripper victim Mary Jane Kelly. The day after the murder he and George Bagster Phillips were employed in sifting through the ashes in the fireplace to determine if there were any burnt organs there, as Kelly's heart was missing. All they found was scraps of woman's clothing.
During the inquest itself there was some vocal criticism by a member of the jury about him being in charge, as the murder had taken place in the jurisdiction of another coroner, Wynne Edwin Baxter. Macdonald dismissed this claim, as the body had been brought into a mortuary in his jurisdiction. The inquest only lasted one day, and Macdonald was later criticized for its brevity and for his methods, which did not include speculating on the time of death or firmly establishing the identity of the deceased.
Macdonald died of cancer in 1894 at the age of 54.