Mitrofan Osipovich Nezhentsev was born on January 28, 1886, into the family of a civil servant, a collegiate assessor. This refutes the widespread myth that the White Movement was solely a struggle of the nobility for their privileges. Nezhentsev was not a nobleman and fought against the Bolsheviks not for privileges, but for Russia, which suffered from the revolution. His place of birth is unknown, but he graduated from a gymnasium in Nikolaev, where he likely spent his childhood. In 1908, he graduated from the Alexandrov Military School in Moscow, and by the beginning of World War I, he had completed two courses at the Nikolaev Academy of the General Staff, which only accepted officers with exceptional abilities. However, the war prevented him from completing his studies.

During World War I, Nezhentsev served in the 58th Prague Regiment on the Southwestern Front, where he proved himself to be a capable commander. His company lost only 22 men in five months of fighting. For this, he was sent to study at the Academy of the General Staff, which he graduated from in 1916, receiving the rank of staff captain and heading the intelligence of the 8th Army.

In May 1917, Nezhentsev presented a report to General L. G. Kornilov on the reasons for the army's passivity and proposed to create a 'shock' detachment of volunteers to counteract the collapse of the front. After receiving an order from Kornilov, he began forming the 1st Shock Detachment of the 8th Army, which became the first volunteer unit in the Russian army. On June 26, 1917, his detachment successfully broke through Austrian positions near Yamnitsa, for which Nezhentsev was nominated for the Order of St. George 4th class.

Nezhentsev's regiment actively participated in combat operations on the Southwestern Front and was located at the Headquarters of the Supreme Commander Kornilov. However, Kornilov refused to involve the regiment in the internal conflict. After the Bolsheviks seized power in October 1917, Nezhentsev became an advocate for armed resistance. He participated in battles against the Bolsheviks in Kyiv and, at the end of 1917, arrived in Novocherkassk, where he reformed the Kornilov Shock Regiment and was promoted to colonel.

In March 1918, when the Bolsheviks were advancing on the Yelisavetinskaya stanitsa, Nezhentsev had to engage the entire regiment in battle. The situation was saved by General Bogaevsky with a counterattack that pushed the Reds back. The next day, the Kornilov Regiment received orders to attack the Black Sea railway station. Nezhentsev's attack was successful, but the regiment encountered strong resistance and suffered losses. Nezhentsev, remaining under fire, continued to command the battle, relying on his authority.

When the Whites managed to seize the artillery barracks, Nezhentsev led the regiment into an attack but was again halted by heavy fire. Realizing that morale was waning, he personally led the regiment into the attack. His last words were: 'Kornilovites, forward!' A Bolshevik bullet struck him in the head, and he fell. He tried to rise, but a second bullet killed him.