For a time d'Entrecasteaux was Assistant Director of ports and arsenals, after which (1785) he was transferred to command a French Squadron in the East Indies. During this service he opened up a new route to Canton by way of Sunda Strait and the Moluccas, for use during the south-east monsoon season. He was then appointed Governor of the French colony of Mauritius.

His explorations

When the expedition left Brest on 28 September 1791, d'Entrecasteaux was promoted to the rank of rear-admiral. The plan of the voyage was to proceed to New Holland (Australia), to sight Cape Leeuwin, then hug the shore closely all the way to Van Diemen's Land (Tasmania), inspect every possible harbour in a rowing boat, and then sail for the Friendly Islands (Tonga) via the northern cape of New Zealand. He was next to follow in La Pérouse's planned tracks in the Pacific. It was thought that La Pérouse had intended to explore New Caledonia and the Louisiades, to pass through Torres Strait, and to explore the Gulf of Carpentaria and the northern coast of New Holland.

However, when d'Entrecasteaux reached Table Bay, Cape Town on 17 January 1792, he heard a report that Captain John Hunter (later to be Governor of New South Wales) had recently seen off the Admiralty Islands canoes manned by natives wearing French uniforms and belts. Although Hunter denied this report, and although the Frenchmen heard of the denial, d'Entrecasteaux determined to make directly to the Admiralty Islands. In so doing, he decided to water and refresh his crew at Van Diemen's Land. On 20 April 1792, that land was in sight, and three days later the ships anchored in a harbour, which he names Recherche Bay. For the next five weeks, until 28 May 1792, the Frenchmen carried out careful boat explorations that revealed in detail the beautiful waterways and estuaries in the area.

D'Entrecasteaux was fortunate in having good officers and scientists, the most important from the exploration point of view being the expedition's first hydrographical engineer, C.F Beautemps-Beaupre, who is now regarded as the father of modern French hydrography. The work this officer did in the field was excellent, and his charts, when published in France as an 'Atlas du Voyage de Bruny-Dentrecasteaux' (1807) were very detailed. The atlas contains 39 charts, of which those of Van Diemen's Land were the most detailed, and which remained the source of the English charts for many years.

Beautemps-Beaupre, with Lieutenant Cretin, while surveying the coasts, discovered that Adventure Bay, which had been discovered by Tobias Furneaux in 1773, was on an island which was separated from the mainland by a fine navigable channel. On 16 May, d'Entrecasteaux commenced to sail the ships through the channel and this accomplished by the 28th. Port Esperance, the Huon River, and other features were discovered, named and charted, the admiral's names being given to the channel and the large island separated by it from the mainland.

On 28 May 1792, the ships sailed into the Pacific to search for La Pérouse. On 17 June, they arrived off the Isle of Pines, south of New Caledonia. From there, d'Entrecasteaux sailed northward along the western coast of New Caledonia, passed the Solomon Islands along their southern or western coasts, sailed through St.George's Channel between New Ireland and New Britain, and on 28 July 1792 sighted the south-east coast of the Admiralty Islands. After three days spent in scrutinizing the eastern and northern coastline, d'Entrecasteaux decided that the rumours he had heard in Table Bay must be false, and he therefore set sail for Amboina, where his ships replenished their stores.

Leaving Amboina on 14 October 1792, d'Entrecasteaux made for Cape Leeuwin to carry out his original instructions of searching southern New Holland for La Pérouse. On 6 December, the land was sighted near Cape Leeuwin, and named D'Entrecasteaux Point. This event was celebrated by feastings and parties, one result of which was that the smith on board La Recherche, Jean-Marie Marhadour, over-indulged and died next day from an apoplectic fit. The weather was boisterous, and the ships failed to find King George III Sound, previously discovered by Vancouver. As they sailed further east, they penetrated numerous islands and dangerous shoals, to which they gave the name D'Entrecasteaux Islands - later changed to the Recherche Archipelago.

While the Frenchmen were still in that dangerous area, on 12 December 1792, a violent storm descended upon them, and both ships were nearly wrecked. Fortunately, however, they found an anchorage where they were able to ride out the worst of the gale. Landings were made here on the mainland, and the locality was named in honour of Legrand, who had spotted the anchorage, and the ship he was on L'Esperance. Beautemps-Beaupre made a hasty survey of the off-lying islands of the archipelago. No water was found, and on 18 December the ships continued eastward to the head of the Great Australian Bight, but here the coast was found to be even more arid, and the water position more serious.

On 4 January 1793, d'Entrecasteaux was forced to leave the coast at a position near D'Entrecasteaux Reef and sail direct to Van Diemen's Land. In this decision the French explorer was unfortunate, for if he had continued his examination of the southern coast of New Holland, he would have made all the geographical discoveries that fell to the lot of Bass and Flinders a few years later. Then, indeed, a French 'Terre Napoleon' might well have become a fact.

The ships anchored in Recherche Bay on 22 January, and a period of five weeks was spent in that area, watering the ships, refreshing the crews and carrying out explorations into both natural history and geography. Beautemps-Beaupre, in company with other officers, surveyed the northern extensions to Storm Bay - the western extension was found to be a mouth of a river and received the name Riviere du Nord - it was renamed the Derwent River a few months later by the next visitor to this area, Captain John Hayes in the Duke of Clarence and the Duchess.

On 28 February d'Entrecasteaux sailed from Van Diemen's Land towards the Friendly Islands, sighting New Zealand and the Kermadecs en route. At the Friendly Islands, he found that the natives remembered Cook and Bligh well enough, but knew nothing of La Pérouse. He then sailed back to New Caledonia, where they anchored at Balade. The vain search for La Pérouse was then resumed to Santa Cruz, then along the southern coasts of the Solomon Islands, the northern parts of the Louisades, through Dampier's Passage, along the northern coast of New Britain and the southern coast of the Admiralty Islands, and thence north of New Guinea to the Moluccas.

By this time, the affairs of the expedition had become almost desperate, largely because the expedition's officers were ardent royalists and the crews equally ardent revolutionaries. Kermadec had died of phthisis in Balade harbour, and on 21 July 1793, d'Entrecasteaux himself died of scurvy, off the Hermits. Commands were re-arranged, with d'Auribeau taking charge of the expedition, with de Rossel in Kermadec's place. The new chief took the ships to Surabaya. Here it was learned that a republic had been proclaimed in France, and on 18 February 1794 d'Auribeau handed his vessels to the Dutch authorities so that the new French Government could not profit by them. D'Auribeau died a month later and de Rossel sailed from Java in January 1795 on board a Dutch ship, arriving at Table Bay in April 1795. There his ship sailed unexpectedly with the expedition's papers, leaving him behind, but this vessel was captured by the British. Rossel then took passage on a brig-of-war, but this too was captured by the British. After the Peace of Amiens in 1802, all the papers of the expedition were returned to Rossel, who was thus enabled to publish a narrative of the whole enterprise.