Career
Mezentsov began his military career in 1845. He participated in the Crimean War of 1853-1856. In 1864, he was appointed Chief of Staff of the Gendarmery Corps.
In 1874, Deputy Chief of Gendarmery.
And finally, in 1876, Chief of Gendarmery and Chief of the "Third Department" (Третье отделение. Political Surveillance and Investigations Department) of His Imperial Highness"s Personal Chancellery.
Mezentsov was assassinated in 1878 by Sergey Kravchinsky.