Robert Mackintosh came from a family of physicians, both on his father and mother's side, extending back to a number of generations. He was born in Valencienne, France, in 1816, while his father Sir William Mackintosh was stationed as surgeon of artillery of the British army, and occupied for three years after the battle of Waterloo a position in the fortresses of France. Later, his father was stationed at Edinburgh, in the military service, where his sons were educated.
He commenced the study of medicine under the preceptorship of his father, who had also an extensive private practice, and was also a prominent lecturer on medicine. He was the author of a popular work on the practice of medicine.
Robert Mackintosh entered the medical department of the Edinburgh University in 1833, and graduated in 1839, receiving his degree as Doctor of Medicine and Surgery. He at once entered into the practice of his profession at Edinburgh, his two brothers became surgeons in the British army.
He arrived in Australia in 1841 where he remained for ten years.
His name was included in the list of Medical Practitioners for New South Wales in 1842.
On the 8th September 1841, he travelled from Stroud to Sydney to testify at the trial of John Kelly who had been accused of the murder of an aboriginal boy Jacky Smith.  Dr. Mackintosh may have taken one of the Steamers that regularly plied between Newcastle and Sydney. Although his travelling expenses for the journey were reimbursed, when he applied to Justice Stephen for remuneration for his attendance as a professional man, his request was denied.
He married Lavinnia Williamson at West Maitland in 1844 . He entered into town life and in April 1845 he was a Judge of livestock at the Hunter River Agricultural Society ploughing match at Maitland.
He was briefly resident in Tamworth as his wife gave birth to their eldest son there on 25th December 1845.
He resided in Sydney in the years 1846 - 1850.
He was elected a District Surgeon of the Sydney Dispensary for Bourke and Macquarie Ward, in the room of Frederick Harpur, Esq., resigned in 1849 
Robert Mackintosh perhaps decided to try his luck on the Gold Fields and joined the many thousands who sailed for California during the Gold Rush. He departed Sydney for California with his friend Dr. Nuttall on the Johannes Sarkies in 1850 .
He eventually established a medical practice in Mission Street San Francisco.
The following hand written note was included in the San Francisco Medical Society records......
In 1892 it was remarked that he was still engaged in active practice, and was probably the only man actively engaged in his profession who was in practice there in 1850