Count Semyon Romanovich Vorontsov (or Woronzow, Russian: Семён Романович Воронцо́в; 26 June 1744 – 9 July 1832) was a Russian diplomat from the aristocratic Russian Vorontsov family. He resided in Britain for the last 47 years of his life, from 1785 until his death in 1832, during which time he was the Russian ambassador to the Kingdom of Great Britain from 1785 to 1800 and to the United Kingdom from 1801 to 1806.

Vorontsov's parents were Roman Larionovich Vorontsov (1717–1783) and Marfa Ivanovna Surmina (1718–1745).^[1] Among his siblings were Imperial Chancellor Alexander Vorontsov, Elizaveta Vorontsova and Yekaterina Vorontsova-Dashkova, the closest female friend of Catherine the Great.^[2]

He distinguished himself during the first Russo-Turkish War at Larga and Kagula in 1770. In 1783, he was appointed Russian minister at Vienna, but in 1785 was transferred to London. Vorontsov soon attained great influence and authority in Great Britain.^[2]

Quickly acquainting himself with the characteristics of English institutions, with their ways and methods, he was able to render important services to his country. Thus, during the second Russo-Turkish War from 1787 to 1792, he contributed to bring about the disarmament of the auxiliary British fleet, which had been fitted out to assist the Turks; and in 1793 obtained a renewal of the commercial treaty between Great Britain and Russia. Over the next three years, he irritated Empress Catherine II with his vehement advocacy of the exiled Bourbons, sharp criticism of the Armed Neutrality of the North, which he considered disadvantageous to Russia, and denunciation of the partitions of Poland as contrary to the first principles of equity and a shock to the conscience of Western Europe.^[3]

Vorontsov married Ekaterina Alekseevna Seniavina (1761–1784), a daughter of Alexei Senyavin and Anna von Bradké. Before her death in 1784, they were the parents of:^[2]

• Mikhail "Michael" Vorontsov (1782–1856), who married Polish Countess Elizabeth Branicka.^[2]
• Yekaterina "Catherine" Vorontsov (1783–1856), who married George Herbert, 11th Earl of Pembroke, 8th Earl of Montgomery, in 1808.^[6]

His wife died on 25 August 1784 in Pisa. Count Vorontsov died on 9 July 1832. He was buried in the Pembroke family vault in Marylebone, London, and the street where he resided in St. John's Wood, London, is now called Woronzow Road.^[1]