He married comparatively early, went to live in neighbouring County Antrim, fathered several legitimate children (Mary, John and Jane), and studied to be a surgeon.
Shortly after their arrival, the commander of the fleet, Governor Arthur Phillip, sent a detachment of guards, convicts and naval personnel – including Jamison – from Sydney Cove to Norfolk Island.
Norfolk Island's remoteness from Sydney enabled Jamison to live openly with a convict mistress, Elizabeth Colley, by whom he had numerous illegitimate offspring.
His lobbying paid off: in 1801, he was appointed Surgeon-General of New South Wales by the British Government, although no date for the start of his commission was specified by the minister responsible, Lord Hobart.
Jamison had returned to Sydney aboard the Hercules in June 1802 after an eventful voyage from London (he had been forced to change ships in Rio de Janeiro because of a heated dispute with the master of his original vessel, Captain Richard Brooks).
[4] Another of Jamison's innovations occurred in 1808, when he and two colleagues undertook a formal examination of the medical competence of William Redfern, who was put forward by the gubernatorial authorities in Sydney as a person fit to perform surgery in the colony.
In 1805, he court-martialled two assistant surgeons for failing to attend women giving birth but this punitive course of action was later over-ruled by the British War Office on a technicality.
Also in 1805, he received a 1,000-acre (4.0 km2) grant of land on the Nepean River, west of Sydney, where he raised livestock and grew crops using assigned convict labour.
William Bligh, the abrasive Royal Navy officer of Mutiny on the Bounty renown, arrived in Sydney in 1806 as the Governor, replacing the less confrontational Philip Gidley King.
In 1807 Bligh added fuel to the fire by sacking Jamison from the magistracy, claiming that the Irishman was not of upright character, and "inimical to the government" because of his dubious trading schemes.
In 1808 Jamison, Macarthur, Blaxcell and other disaffected colonists joined forces with the New South Wales Corps to arrest and expel Bligh from Government House in a military coup d'état that has now become known colloquially in Australia as the Rum Rebellion.
[5] Jamison left Sydney for London in 1809, with some of the other mutineers, to safeguard his financial affairs and testify against Bligh at any legal proceedings that might arise as a consequence of the governor's overthrow.
[6] Jamison's death denied him the opportunity to give evidence at the trial of Major George Johnston, of the New South Wales Corps, who had been a ring leader of the anti-Bligh plot.