He was the brother-in-law of
Ralph Darling. When Darling was appointed
Governor of New South Wales, in 1824, Dumaresq was already serving as Darling's Military Secretary in
Mauritius. He was appointed Darling's Private Secretary, and arrived in New South Wales, five months before Darling, to prepare for Darling's arrival. He was subsequently appointed clerk of the
Executive Council. His brothers,
William and
Edward, also followed Darling and their sister,
Eliza, to Australia. William went to New South Wales, but Edward went to Tasmania—then called
Van Diemen's Land—where he became acting
Surveyor-General, in 1825. Darling had been appointed with the objective of restoring discipline to the penal colony, after what was seen by the British government of the time as the relatively lax rule of the two previous Governors,
Lachlan Macquarie and
Thomas Brisbane. As such, he had the support of the 'Exclusives' faction in the colony, who had sought to undermine Brisbane's administration. Darling tended to rely upon like-minded military men for his administration, and it was soon subject to criticism for nepotism and favouritism. This criticism could not be stifled, as Darling's predecessor,
Thomas Brisbane, had ended press censorship, creating in effect
press freedom before Darling arrived in 1824. Darling's subsequent attempt to control the press through new legislation failed, because the Chief Justice,
Francis Forbes, advised that the measures were not compatible with the laws of England. The Dumaresq brothers, Henry in particular, became a lightning rod for criticism of Darling's administration. He fought a duel with barrister and newspaper editor
Robert Wardell in 1827, over an article in Wardell's newspaper,
The Australian, titled "
How-e to live by plunder", with both men leaving uninjured. Dumaresq had arrived in the colony as a single man. His sister, the Governor's wife,
Eliza Darling, tried unsuccessfully to arrange a match between Dumaresq and her friend,
Fanny Macleay, daughter of
Alexander Macleay. Later in 1827, he went to England, where he married Elizabeth Sophia Butler-Danvers, half-sister to the 5th
Earl of Lanesborough. He and his new wife returned to New South Wales, in 1829, bringing with them a
royal charter for an expanded
Legislative Council. The couple had four daughters and three sons. A visitor to the colony in 1832, Edmond de Boissieu, of the French ship
La Favorite commanded by
Cyrille Laplace, recorded prevalent gossip in the colony that Dumaresq was having an affair with Mary Jones, the wife of the Sydney merchant,
Richard Jones. By the time that Darling's term as governor ended in 1831, Henry and his brother William had been granted substantial landholdings in New South Wales. Henry had a property near modern-day
Muswellbrook, that he named St Heliers. He also operated a large sheep run in the New England region,
Saumarez, from 1835; The new Surveyor-General
Sir Thomas Mitchell developed a strong resentment of Darling and his relatives. The source of this resentment was his belief that a task given to him —surveying the
Great North Road—was prioritised to allow
Eliza Darling to more easily visit her brothers' properties in the Hunter Valley, while Charles Sturt (a cousin of Henry Dumaresq's wife) led an
exploratory expedition that Mitchell considered should be his due to his position. Henry's brother William, was Acting Deputy Surveyor-General but retired soon after Mitchell was promoted as his superior, in 1829. After Darling left the colony, Henry Dumaresq continued to serve as Private Secretary for Acting Governor
Patrick Lindesay, but retired from public office once the new governor, liberal-minded
Richard Bourke, arrived. After retiring from his public duties, Dumaresq still had the benefit of his large landholdings, which were praised as models of well managed estates by visiting colonists.
Francis Forbes view that Henry and William Dumaresq were
"obviously expectants of what may first fall" was justified; both men prospered greatly from colonial appointments and by land grants made under the Darling administration. Both would be wealthy men for the rest of their lives. == Later career and death ==