Dmitry Semyavin was born in the estate of Komlevo in the Borovsky district of the Moscow province, which later became part of the Kaluga region. He came from the noble family of Semyavins, known for their traditions of service in the navy. His father, Nikolai Fyodorovich Semyavin, was a retired premier-major and served for some time as an adjutant to his cousin Alexei Naumovich Semyavin.

In 1773, when Dmitry was 10 years old, he was enrolled in the Naval Cadet Corps in St. Petersburg. Four years later, in 1777, he received the rank of midshipman and participated in training voyages in the Baltic Sea. On May 1, 1780, after passing his exams, Semyavin became a lieutenant and was assigned to the ship "Prince Vladimir."

In 1780-1781, he served in the Russian squadron off the coast of Portugal, supporting armed neutrality during the American War of Independence. In 1782, Semyavin began service in the Azov military flotilla, where he initially served on the corvette "Khotin." In 1783, he was promoted to lieutenant and became a flag officer under Rear Admiral F. F. Mackenzie. He participated in the construction of the Akhtiar port in Sevastopol and commanded the packet boat "Karabut," carrying out important diplomatic missions.

With the start of the Russo-Turkish War in 1787, Semyavin held the rank of captain-lieutenant and received the Order of St. George 4th class for successful operations. After the victory at Ochakov, he was sent to St. Petersburg to report to Catherine II about the victory. Despite his achievements, he had a strained relationship with Commander Fyodor Ushakov, which once led to his arrest.

During the second phase of the war, Semyavin became a captain of the 2nd rank and an adjutant to Prince Grigory Potemkin. He commanded several ships and participated in the battle at Cape Kaliakria and the battle at Varna. By the beginning of the War of the Second Coalition against France, he was a captain of the 1st rank and commanded the battleship "St. Peter." In 1798, he successfully attacked the fortress of St. Maura and participated in the siege of Corfu.

After the military campaign ended in 1800, Semyavin was appointed commander of the port of Kherson, and later Sevastopol. In 1804, he became a rear admiral and head of the fleet in Revel. In 1805, having attained the rank of vice-admiral, he led the Russian squadron in the Mediterranean to counter the French. He successfully conducted several operations against the French in the Adriatic and captured the fortress of Bocca di Cattaro.

With the start of the Russo-Turkish War in 1806, Semyavin directed the squadron to the Aegean Sea and established a blockade of the Dardanelles. In 1807, he achieved victories in the Dardanelles and Athos battles, allowing the Russian fleet to control the Aegean Sea. However, after the Treaty of Tilsit, Semyavin was forced to cease military operations and cede the Ionian Islands to France.

In 1807, his squadron found itself in a difficult situation in Lisbon, blocked by the English fleet and occupied by the French. Semyavin managed to save his ships by concluding a convention with the English, under which the Russian squadron went to England until peace was concluded. In 1809, Semyavin returned to Russia but fell into disgrace and was demoted.

During the Patriotic War of 1812, his squadron patrolled the shores of England. In 1813, Semyavin was retired, which created financial difficulties for his family. Only in 1825, with the accession of Nicholas I to the throne, did he return to service and become commander of the Baltic Fleet. In 1826, Semyavin was promoted to admiral and awarded for his merits. Dmitry Nikolaevich died on April 5, 1831, and was buried in St. Petersburg.