In December 1816 he was demoted to Private by the order of Grand Duke Konstantin Pavlovich for "rude behavior in the house of a collegiate assessor, Mrs Wangersheim, not paying his debt to a candy shop, and laziness in military service".

He shot and fatally wounded the governor of Saint Petersburg and a popular hero of the Napoleonic Wars, General Mikhail Andreyevich Miloradovich, who attempted to pacify the Decembrists troops and prevent the bloodletting.

Kakhovsky also killed the commander of the Life-guard grenadier regiment colonel Ludwig Niklaus von Stürler who went to the Senate Square to persuade his soldiers not to take part in the uprising, and wounded another officer Gastfer.

He argued before the Investigating Commission, that the high-handedness of the bureaucracy, the lack of respect for ancient gentry freedom, and the favoritism shown to foreigners had been the primary cause of the suppressed uprising.

He was executed (at the second attempt) along with four other ringleaders—Pavel Pestel, Sergey Muravyov-Apostol, Mikhail Bestuzhev-Ryumin and Kondraty Ryleyev on a crownwork of the Peter and Paul Fortress on 25 July 1826, and presumably interred with the rest of the five in a secret grave on Goloday Island in Saint Petersburg.

His grandniece Irina Konstantinovna Kakhovskaya (1887 – 1960) was a Left Socialist-Revolutionary militant and also became a terrorist: in 1918 she collaborated in the assassination of the German governor of Ukraine Hermann von Eichhorn, and actively worked in two failed attempts on the lives of Hetman Pavlo Skoropadskyi and General Anton Denikin.