Born in a family estate near Borovsk, Senyavin belonged to a notable family of sea captains, all of whom, starting with his great uncle, served in the Imperial Russian Navy. Having graduated from the Naval Corps in 1780, he took part in an expedition to Lisbon, then joined the Black Sea Fleet upon its formation in 1783 and helped construct the naval base in Sevastopol. Family interests gained him rapid promotion, especially after his resolute actions had prevented a flagship from capsizing during the Varna expedition and Prince Potemkin had entrusted him with a vital task of transporting diplomatic mail to the Russian embassy in Constantinople.
During the Russo-Turkish War, Senyavin was present at Fidonisi and Ochakov and went to Saint Petersburg to inform the Empress about the former victory. Although he distinguished himself in command of the battleship Navarchia during the Battle of Caliacria, he had no patience with Ushakov's cautious and cunctative approach and paid little attention to his authority, which resulted in his confinement to a guardhouse and the threat of his reduction in rank. At last Potemkin effected a reconciliation between Senyavin and his peer, remarking in his letter to Ushakov that Senyavin could become the greatest admiral that Russia had ever known.
During Ushakov's Mediterranean Expedition of 1798-1800, Senyavin assumed command of the flagship Saint Peter, equipped with 72 guns. His sailors stormed the French fortress of Saint Maura in Lefkada and took part in the capture of Corfu. The expedition over, Senyavin administered the ports of Kherson and Sevastopol. In 1804, he was promoted to Rear Admiral and given the task of administering the port in Reval.
Three years later, Alexander I of Russia, still entertaining grand designs aimed at stalling Napoleon's expansion in the Adriatic, mounted another Mediterranean expedition, with Vice-Admiral Senyavin as Commander-in-Chief. By September 1806, Senyavin reasserted Russian control of the southern Adriatic, disrupted Dubrovnik's sea trade, and was poised to attack Lesina. He found a natural ally in the Orthodox princes of Montenegro, who pledged to support him on land.
The Russian fleet captured the islands of Curzola and Lissa, while the Austrians were persuaded to surrender Cattaro to them. As a result of these operations, the French were prevented from taking hold of the Ionian Islands. However, the fruits of Senyavin's activity were thrown away by the tsar who would conclude the Treaty of Tilsit with Napoleon the following year.
Even before the treaty was negotiated, a new war with Turkey had erupted and Senyavin's squadron was ordered to proceed to the Aegean Sea in order to attack Istanbul. He reached the Dardanelles on February 24, 1807 and captured the island of Tenedos in March. Using the island as his place d'armes, Senyavin blockaded the Straits and cut off supplies to the Sultan's capital.
Contrary to his expectations, Sir John Thomas Duckworth, a British admiral who had just lost 600 men under fire of the shore batteries, refused to join his own fleet with Senyavin's and embarked upon an ill-fated expedition to Alexandria. The Russians were to fight the outnumbering Turks in the Aegean without foreign support.
Senyavin's blockade of their capital eventually drove the Turks to extremes. After food riots broke out, Sultan Selim III was replaced with Mustafa IV, who ordered his fleet to break the blockade. The Ottoman ships clashed with Senyavin's squadron in the Battle of the Dardanelles (May 11) and Battle of Athos (June 16). Both engagements were Russian victories and ensured Russia's ascendancy in the Aegean for the rest of the war.
Upon receiving news about the Treaty of Tilsit, Senyavin was reported to have been overcome with tears (12 August). All his conquests had to be forfeited after the international situation had been reversed dramatically: Napoleon was considered Russia's ally and Britain was Russia's foe. On 14 August he and Lord Collingwood reluctantly parted ways. Eight days later, a large part of the Russian squadron (5 battleships, 4 frigates, 4 corvettes, 4 brigs) was ordered to return to Sevastopol. Senyavin was to lead the remaining fleet to the Baltic, where the Finnish War with Sweden was already brewing.
Tenedos was evacuated on 25 August and Senyavin set sail from Corfu on 19 September. Although he planned to proceed directly to Saint Petersburg, stormy weather induced him to enter the Tagus River and cast anchor in Lisbon on 30 October. Within several days, John VI of Portugal fled to Brazil and the Royal Navy blockaded Lisbon, intercepting a Russian sloop as an enemy vessel: the Anglo-Russian War had been declared. In November, French forces under Duc d'Abrantès overran the Portuguese capital and Senyavin found himself wedged between two warring powers.
In this tricky situation, Senyavin distinguished himself as a skilled diplomatist and managed to save his ships from destruction. Upon hearing about his plight, Napoleon extorted from the tsar the privilege of giving orders to Senyavin through the Russian embassy in Paris. He immediately demanded to replace British officers serving in Senyavin's squadron with the French or the Germans and advised Senyavin to exchange several ships with Duc d'Abrantès. Napoleon's orders were politely ignored by the Russian admiral, who had no intention to risk the lives of his marines in pointless warfare against erstwhile friends and consequently professed his neutrality.
In July 1808 Senyavin's ships, still blockaded in Lisbon, were repeatedly visited by Duc d'Abrantès and Duc de Valmy, who exhorted him to assist in their military operations against the Portuguese and the Spaniards. To that Senyavin responded that he had not been authorized by the tsar to fight the peoples his country was not at war with and neither promises nor threats could make him change his mind.
In August the French were beaten by the Duke of Wellington at Vimeiro and were compelled to leave Portugal. Senyavin's seven battleships and one frigate were left face to face with 15 British battleships and 10 frigates, to say nothing about coastal artillery. They could have easily annihilated the Russian squadron if Senyavin refused to surrender. The Russian admiral, however, maintained his neutrality, threatening to blow up the ships and set Lisbon ablaze in case of attack. At last a convention was signed with the British admiral, Sir Charles Cotton, whereby the Russian squadron was to be escorted by the Royal Navy to London without lowering Russian flags. Moreover, Senyavin was to assume supreme command of the joint Anglo-Russian fleet (as the senior officer of the two), while two Russian ships (Rafail and Yaroslav) were to be left in Lisbon for repairs.
On 31 August Senyavin's squadron embarked from Portugal for Portsmouth. On 27 September the Admiralty was informed that enemy vessels cast anchor in the British harbour, with their flags streaming, as if in times of peace. The Lord Mayor of London declared the convention disreputable for Britain's prestige and many in the Admiralty shared his opinion. The Russian fleet was therefore detained in Portsmouth under various pretexts until winter weather made their return to the Baltic impossible. The British insisted that Senyavin's squadron should sail to Arkhangelsk, else they would be intercepted by the Swedish men-of-war. In 1809, the departure was further delayed by the disastrous British expedition to Flushing. At long last, on 5 August, the nearly-starved Russian fleet was allowed to leave Portsmouth for Riga, where they arrived on 9 September, 1809.
Senyavin's disobedience to the Emperors resulted in his not being employed again at sea. During Napoleon's invasion of Russia, he administered the peaceful port of Reval and was given no chance to take part in hostilities, despite his regular petitions to let him muster a militia in his native province.
Although he settled into retirement in the next year, Senyavin's name remained so popular in the Navy that the Decembrist conspirators planned to make him a member of the Provisional Government after staging a palace revolution. When the Greek War of Independence broke out in 1821, Greek insurgents requested the tsar to send "the famous Senyavin" to their assistance, but their petition was rejected.
It was not until Alexander I's death in 1825 that Senyavin was recalled to active service. As Russia was preparing to resume hostilities against Turkey, Nicholas I of Russia appointed him to command the Baltic Fleet. The following year, he was promoted Full Admiral and accompanied Login Geiden's squadron heading for the Mediterranean, where combined Anglo-Franco-Russian forces would score the great victory at Navarino.
Dmitry Senyavin died three years later and was interred with great pomp, in the presence of the tsar, at the Alexander Nevsky Lavra. He had several ships named after him in the Imperial and Soviet navies, notably the vessel used for the three-year expedition ordered by Czar Nicolas I in 1826. The Senyavin Islands in Oceania and the promontories in Alaska and Sakhalin still commemorate his name.