After graduation from the Vladimir of Kiev Cadet Corps and elite Nicholas Cavalry College [ru], he joined the Imperial Russian Army at age 18 as a cornet in the 12th Hussars Regiment.

During the Russo-Japanese War (1904–1905), Samsonov commanded a cavalry brigade of the Ussuri Siberian Cossack Division.

[2] Through these conflicts Samsonov gained a reputation as an energetic and resourceful leader, but some observers criticized his strategic abilities.

This antagonism is said to have been based on an incident after the Battle of Liaoyang during the Russo-Japanese War where Samsonov had publicly quarrelled with Rennenkampf on the landing platform of a railway station, and that the two were mutual lifetime enemies.

[7] However, the original source of this story is considered to be Max Hoffmann, at that time a colonel on the staff of the German Eighth Army.

[9] Hoffman appears to have advanced this story during planning sessions, in support of his argument that Rennenkampf would not come to the aid of Samsonov.

[10] Hindenburg and Ludendorff arrived on the Eastern Front and decided to attack Samsonov's advancing forces with the full weight of the Eighth Army.

The rout that followed was named the Battle of Tannenberg by Hindenburg, to compensate for a defeat of the Teutonic Knights by the Kingdom of Poland and the Grand Duchy of Lithuania at the same location five centuries earlier.

[14] Samsonov and a small group of staff officers and men attempted to escape the encirclement, at first on horseback, and then on foot, over swampy ground, in the darkness of the night of August 29.

[14] A German search party eventually found Samsonov's body in the adjacent forest, a bullet wound in his head and a revolver in his hand.