Souchon entered the navy in 1881, and in December 1888 saw action on board the Adler off Apia, Samoa.
From 1896 to 1900 he served with the Supreme Command of the Navy, and from 1902 to 1904 with the Admiralty Staff. Souchon was chief of staff of the East Asian Cruiser Squadron during the Russo-Japanese War. After a brief tour in 1908 as captain of the battleship Wettin, he became chief of staff of the Baltic Sea naval station at Kiel in 1909; two years later he was promoted rear admiral in this capacity.
The outbreak of the war found Souchon as chief of the German Mediterranean Squadron, consisting of the battle cruiser Goeben and the light cruiser Breslau. On August 4 he bombarded the French Algerian ports of Bone and Philippeville and then headed to Messina to recoal. There an Allied force should have intercepted him had it not been for the incredible bungling both at the Foreign Office and at the Admiralty in London. Instead, between August 6 and 10 Souchon managed to evade Allied ships and to break through to Constantinople, despite serious boiler leakages in the Goeben. The decision to make for the Porte had been reached on August 3 by Admirals Hugo von Pohl and Alfred von Tirpitz without consulting the kaiser. At Constantinople, the German ships were renamed Sultan Yavuz Selim and Midilli while Souchon became supreme commander of the Turkish navy on August 16. No doubt influenced by the arrival of the two German ships, Turkey declared for the Central Powers in October 1914. Souchon boldly raided the Russian Black Sea port of Sevastopol on October 29 and clashed with superior Russian naval forces off Balaclava (November 18), Batum (December 10), and in the Bosphorus (December 26). He was promoted vice admiral in January 1915 and awarded the order Pour le mérite in October 1916.
Souchon returned to Germany in September 1917 and took command of the Fourth Squadron of the High Sea Fleet. He led these latest dreadnought battleships the following month during the German conquest of the Russian Baltic Sea islands of Osel, Moon, and Dago. Promoted admiral on August 11, 1918, he was placed on the inactive list during the overall naval reorganization conducted by Admiral Reinhard Scheer of the new Supreme Command of the Navy in order to make room for younger, more energetic flag officers. On October 30, however, Souchon was reactivated and appointed chief of the Baltic Sea naval station. It was an unfortunate decision: that very day sailors on the fleet rebelled rather than take part in a planned death ride against the British Grand Fleet. Souchon therefore arrived at Kiel at the height of the rebellion; he quickly yielded to the Social Democrat Gustav Noske, who managed to restore order in the port. Souchon retired on March 17, 1919, to St. Magnus near Bremen until his death in 1946.