In 1782, he joined the Irish Volunteers, one of the local regiments formed during the American Revolutionary War, to defend Ireland against invasion from France; his commission as a junior officer was signed by George III.
He qualified as a "Mate to Indiamen", eligible to work with the East India Company, once he had twelve months practical experience "walking the wards" in one of London's large charity hospitals.
He attended lectures by other prominent physicians including John Hunter, and dissections held in the Company of Surgeons' anatomy theatre at the Old Bailey.
On each occasion his defaulter either failed to appear to prosecute him, found himself unable to positively identify D'Arcy Wentworth, or sought only to name and shame him.
In March 1787, Fitzwilliam's patronage secured Wentworth a direction from the Home Office, to leave without delay for Portsmouth, where the First Fleet was making ready to sail to Botany Bay.
Five weeks after the Neptune arrived, to avoid a worsening disaster, Governor Arthur Phillip sent nearly 200 convicts and their superintendents to Norfolk Island on the Surprize, en route to China.
[10][11] In June 1793, Earl Fitzwilliam offered him a lifeline; he appointed his London lawyer, Charles Cookney, Wentworth's agent, making it possible for him to become an early trader in the Colony.
The second governor, Captain John Hunter, gave Wentworth permission to leave Norfolk Island, and he arrived back in Sydney on 5 March 1796.
In London, Earl Fitzwilliam pursued the matter of payment for his service as Assistant Surgeon, and in 1798, as a result of his efforts, Wentworth was paid arrears of £160, for six years work.
In Sydney, Hunter allowed several people, including Wentworth, to act as traders, in an attempt to break the power of the Rum Corps officers through competition, and to lower the price of commodities.
On 11 May 1799, he appointed Wentworth Assistant Surgeon at Parramatta, in charge of the hospital there, replacing James Mileham, who was later court martialled for refusing to attend the settlers, free people, and others.
On 15 April 1800, King returned to Sydney from London with a dormant commission, to act as governor in the case of the death or during the absence of Captain John Hunter.
As a consequence of Bligh's belligerence, Wentworth supported Major George Johnston and John Macarthur in the Rum Rebellion on 26 January 1808, that overthrew the Governor and placed him under house arrest.
They recognized that reason, science, and an exchange of ideas, knowledge and experience were necessary to progress the Colony and to achieve Macquarie's vision for a more harmonious and inclusive society.
[33] Macquarie signed the contract for construction of a new hospital on 6 November 1810, with a consortium of businessmen – Garnham Blaxcell and Alexander Riley, later joined by D'Arcy Wentworth.
Historian James Auchmuty commented that "despite his general popularity, comparative wealth and powerful connexions at home, Wentworth mixed little in non-official social life," observing, "the liberal views imbibed in the Ireland of his youth," which had "resulted in more than usual sympathy with the convict population," and "the circumstances of his personal life in the Colony prevented him from fully sharing in the social round.
In consequence of there being neither gold nor silver coins of any denomination, nor any legal currency, as a substitute for specie in the colony, the people have been in some degree forced on the expedient of issuing and receiving notes of hand to supply the place of real money, and this petty banking has thrown open a door to frauds and impositions of a most grievous nature to the country at large…At present the agricultural and commercial pursuits of the territory are very much impeded and obstructed by the want of some adequately secured circulating medium.
In February 1817, the Bank of New South Wales was established; Macquarie gave it a Charter as a joint stock company, providing its directors with limited liability.
[38] The new bank facilitated financial transactions and encouraged commerce; it helped bring to an end the Colony's dependence on rum as money, and the need for dubious promissary notes.
In his third despatch to London, written on Easter Monday 1810, Macquarie reported on what he saw was the Colony's most pressing problem:"I was very much surprised and Concerned, on my Arrival here, at the extraordinary and illiberal Policy I found had been adopted by all the Persons who had preceded me in Office, respecting those Men who had been originally sent out to this Country as Convicts, but who, by long Habits of Industry and total Reformation of Manners, had not only become respectable, but by Many Degrees the most Useful Members of the Community.
His approach startled and dismayed the Exclusives and wealthier free settlers, and met immediate opposition within the barracks, from the officers of the 73rd Regiment, sent to the Colony to replace the discredited Rum Corps.
In London, Opposition support for their campaign spurred the Secretary of State, Earl Bathurst, to propose in April 1817: "the appointment of commissioners who shall forthwith proceed to the settlement with full powers to investigate all the complaints which have been made, both with respect to the treatment of convicts, and the general administration of the government.
"[41] Nearly two years later, on 19 January 1819, John Thomas Bigge was appointed Commissioner of Inquiry, with a private instruction from Earl Bathurst to end Macquarie's dream of an inclusive society in the Colony.
At day break on 12 February 1822, with his wife Elizabeth and son Lachlan, he passed through an "immense concourse" to the harbour, filled with "a great gathering of launches, barges, cutters, pinnaces and wherries", and went aboard the Surry, for the voyage home.
[47] At his farewell dinner, Governor Brisbane, in defiance of the Exclusives and the Bigge Report, recognised the importance and significance of the Emancipists, and he undertook to champion their cause with the British Government.
D'Arcy initially led the protagonists supporting freedom of the press, a fully elected representative government for the Colony, and no taxation without representation.
[50] In 1807, Fitzwilliam, appalled by reports of Bligh's behaviour towards D'Arcy Wentworth,[51] applied to Viscount Castlereagh, Secretary of State for the Colonies, for him to be given leave of absence to return to London.
Fitzwilliam wrote again the following year, to inform Castlereagh that Wentworth had been: "suspended from the duties of his office & consequently from its emoluments, this devoted man is retained a prisoner in the Colony.
On Monday 9 July, despite dreadful weather and the risk of influenza, a funeral procession more than a mile long, with forty carriages and more than fifty men on horseback, accompanied his hearse on its journey to Parramatta.
[58] The Australian noted his reputation as a doctor and as a magistrate: "As a medical practitioner, Mr Wentworth was distinguished for his tenderness with which he treated his patients of every degree, and that class of unfortunate persons whom the charge of General Hospital placed so extensively under his care.