He sometimes signed his full surname, Alcalá-Galiano, but often used just Galiano. The published journal of his 1792 voyage uses just the name Galiano, and this has become the name by which he is most known.
He participated in several hydrographic surveys and became skilled in cartography. As a junior officer he spent time in the River Plate region and the Falkland Islands. He returned to Spain in 1783.
In 1784 Galiano met and worked with Alessandro Malaspina, with whom he would later journey to America. Both men were among a group of officers studying astronomy at the Royal Observatory in Cádiz under Admiral Vicente Tofiño. The association was brief, as Tofiño was called upon to create an atlas of the coast of Spain, and he chose Galiano to work on the project. Thus Galiano assisted Tofiño's great hydrographic study, which resulted in the Atlas Maritímo de España, published in 1789. This experience was the basis of Galiano's expertise as a professional cartographer.
In 1785 Galiano married María de la Consolación Villavicencio. Soon after the marriage he left on a survey of the Strait of Magellan under another influential teacher, Antonio de Córdoba.
In 1788 he was given charge of a mission to fix the location of the Azores, during which he was in command of the brig Natalia. In the same year he assisted in the final stages of Tofiño's mapping project.
The expedition arrived in Acapulco in March, 1791. Galiano was put in charge of a group of Malaspina's scientific officers assigned to stay in Mexico for a year. Malaspina's letter to the viceroy of New Spain, Juan Vicente de Güemes, Count of Revillagigedo, read in part: Under the orders of Ship Lieutenant Don Dionisio Galiano, he, together with [Novales, Pineda, and Olavide], will proceed to [Mexico] ... [Galiano] will be charged with coordinating in that capital, and later in Spain, all the notes of our past tasks ... Besides, he must extract all that information conducive to giving an exact idea of the former and present state of [New Spain].
Thus Galiano remained in Mexico, compiling the expedition's hydrographic and astronomical data, and making maps. He also investigated the colonial archives and collected information useful in assessing the state of the colony. This was one of the political tasks of the Malaspina expedition, for which Malaspina and his officers had royal authority above that of the viceroy, authorizing access to any and all documents they might think relevant. He spent about a year at this task, while the Malaspina expedition sailed to Alaska and Vancouver Island.
The expedition left Acapulco on March 8, 1792. Galiano commanded the Sutil, and the expedition overall, while Valdés commanded the Mexicana. These ships were "goletas", a Spanish term often translated as "schooner". However goletas were not necessary rigged as schooners. The Sutil was rigged as a brig and the Mexicana began rigged as a topsail schooner but was changed during the voyage to a brig.
On June 3 a group of Nuu-chah-nulth asked Quadra for help against a ship that had attacked a village in Esperanza Inlet. They said that seven of their people had been killed, many wounded, and all their sea otter furs seized. Quadra had his surgeon tend some of the wounded and promised to punish the aggressors. Galiano was under the impression that the ship was the Columbia Rediviva under Robert Gray, but the attack was actually done by the English fur trader William Brown. Brown was the commander of three trading vessels, the Butterworth, Jackall, and Prince Lee Boo, collectively known as the Butterworth squadron. He had a grant from the British government to set up a fur trading post on the coast of Vancouver Island. It was expected that Spain would turn over the post at Nootka Sound to the British later in the year, but due to Quadra's firm stand the transfer did not happen. Brown may have been planning to take over the post, but instead did not establish any post. Later in the year Brown had a violent conflict with the indigenous people of Clayoqout Sound as well. He claimed he acted in self-defense, while other fur traders said he forcefully stole furs from the Clayoquot people.
On May 18 and 28 the Spanish made an observation of the moons of Jupiter, allowing them to finely calibrate their chronometers. Two other chances to make the observation failed due to cloudy skies.
Having with them maps and information about the Strait of Juan de Fuca obtained by Quimper in 1790 and Eliza in 1791, Galiano intended to sail quickly to Bellingham Bay and then north into the Strait of Georgia. In accordance with his orders, Galiano was most interested in unexplored waters that extended east into the continent. For that reason he opted not to explore the south-tending Boca de Caamaño (Admiralty Inlet), which would have led him into Puget Sound. In any case, George Vancouver had just finished his exploration of Puget Sound when Galiano and Valdés were sailing into the Strait of Juan de Fuca.
The Sutil and Mexicana left Neah Bay on June 8, crossing to the north side of the Strait and cruising along the coast of Vancouver Island. They sailed through the night, reaching Race Rocks around dawn, then made for Esquimalt Harbour (Puerto de Córdova). Tetacus suggested a place to stop and take on water, there being fewer sources near Esquimalt Harbour. Galiano and Valdés were impressed by Tetacus in many ways. He knew the names of all the Spanish and British captains who had been to the region, and said that two ships had already entered the Strait of Juan de Fuca — these being the ships of George Vancouver. Tetacus was also shown a map of the Strait of Juan de Fuca and recognized many places and told the Spanish what the native names were. He was one of the region's more powerful chiefs, more or less of the status of Maquinna and Wickaninnish.
The Spanish anchored in Esquimalt Harbour around noon on June 9. Soon two of his wives arrived by canoe. They had followed from Neah Bay by canoe, not wanting to sail on the Spanish ships. In the evening the Spanish officers went the villages on shore. Galiano thought that Tetacus was the chief of these villages, but it is unlikely that they were his people since they were in the territory of the Songhees while Tetacus was a Makah. He may have been a relative. José Cardero, an artist who accompanied Galiano and Valdés, drew portraits of Tetacus and two of his wives. One of his wives is shown wearing Coast Salish dress. She may have been a Songhees woman.
The Spanish ships left Esquimalt very early on June 10. They made for Smith Island (Isla de Bonilla) and, after sighting it, turned to the north, making for Lopez Island. They anchored near Point Colville at the southern end of Lopez Island. A party was sent ashore to make an observation of the first moon of Jupiter, by which they were able to improve their longitude measurements. The next day they sailed northeast through part of Rosario Strait and through Guemes Channel into Padilla Bay, noting a village on the shore of Guemes Island. That evening they anchored in Bellingham Bay (Seno de Gaston).
Since Galiano had set out from Nootka while Vancouver had entered the Strait of Juan de Fuca directly from the south, Galiano and his crew became the first Europeans to circumnavigate Vancouver Island. They were also the first Europeans to discover and enter the Fraser River, on June 14, 1792.
Galiano had received letters of suggestion and order from both Malaspina and Viceroy Revillagigedo. Malaspina urged a stop at San Francisco on the return, in order to map and assess the Spanish colony there, which Malaspina's expedition had been unable to do. The viceroy, while not directly contradicting Malaspina, informed Galiano of the "almost continuous fog" at San Francisco and the lack of provisions compared to Monterey. Careful not to give contrary orders, the viceroy strongly suggested that Monterey would be a better place to stop than San Francisco. As it turned out, Galiano stopped at Monterey and not San Francisco, due to incliment weather. Both Malaspina and the viceroy also urged Galiano to investigate the "Entrada de Ezeta" (the mouth of the Columbia River), which the Spanish expedition of Bruno de Heceta (also spelled Ezeta) had sighted in 1775, but had been unable to enter or even determine whether it was a river or a strait. At Nootka Sound Galiano learned from Juan Francisco de la Bodega y Quadra that Robert Gray had already entered the river. Quadra had given Galiano a sketch map of the river's mouth based on Gray's information. Galiano sighted the Columbia River on September 8, 1792. He did not enter the river, claiming that his ships were inappropriate for the task. However he did fix the location and determine that is was a river and not a strait.
Galiano returned to Mexico in late 1792 and began to write an account of his explorations, which was published in 1802, unusual in that Spain typical kept its exploration results secret. Galiano would likely have remained obscure if not for his exploration of the Strait of Georgia and Vancouver Island.
In 1795 Malaspina was imprisoned for plotting against the state. Spain had planned to publish a grand report and atlas about his expedition, but after his political downfall this became impossible. After reports of the voyages of La Pérouse and George Vancouver were published in 1797 and 1798, the Spanish authorities, unwilling to publish Malaspina's report, which would have surpassed any other, settled on publishing only the account of Galiano's expedition. Malaspina's name was totally removed and the fiction that Galiano operated under the direction of viceroy Revillagigedo was inserted. In effect Galiano replaced Malaspina as Spain's great explorer of the late 18th century.
Alessandro Malaspina returned to Spain in August of 1794. Galiano joined him in presenting the Malaspina expedition's report to the Commander in Madrid. Along with two other officers they stayed in the capital to prepare a planned publication compiled from the vast quantity of reports, observations, charts, drawings, and other data collected during Malaspina's five-year voyage. This massive undertaking, which was to include a grand narrative and an atlas, was intended to rival the publication of the expeditions of James Cook. Galiano's 1792 exploration of the Strait of Georgia was to be an important complement to the accounts of Malaspina's visits to Alaska and Nootka. However, Malaspina tried to influence Spanish politics regarding the American colonies with disasterous consequences. He was arrested in late 1795 and imprisoned from 1796 to 1802, after which he was exiled from Spain. Nearly all documents from his expedition were seized and publication forbidden. As a result, Galiano's account of his exploration, published in 1802, became the only Spanish publication about Spanish activities in the Pacific Northwest for many years, and Galiano's name became synonymous with Spanish exploration of the region.
After this, Galiano returned to cartography and then active duty as war broke out with Britain. Careful to distance himself from Malaspina, Galiano remained untainted by the political disaster. In 1797 he was in command of the frigate Vencedor during the Battle of Cape St Vincent.
In 1798 Galiano went with a group of ships to America to bring treasure to Spain, much needed for war funding. He slipped through the British blockade of Cádiz at night during a storm, then sailed to the Caribbean, picking up silver and other valuables at Cartagena and Veracruz. Returning, he had to evade enemy ships several times, but reached Cádiz safely. He made a second treasure voyage to New Spain and commanded of a small squadron on the return voyage. British ships and bad weather drove him into Havana, where he was when the Treaty of Amiens ended the war in 1802.
In December 1804 war broke out again between Spain and Britain. Galiano, now a brigadier, was given command of the 76-gun ship Bahama. he fought in the Battle of Trafalgar, where he was killed by a cannonball on October 21, 1805. His body was buried at sea from his half wrecked ship.