In 1823, he joined the Southern Society of Decembrists and became one of the main assistants to Sergey Muravyov-Apostol on Vasilkovskaya Uprava of the South society. He was a participant in conferences of the Southern society in Kiev and Kamenka, and negotiated with secret Polish society. He was the author of the Decembrists' Proclamation that was read to the troops and local peasants. He also was known to dress in the clothes of lower classes and agitate people to revolt against the monarchy. Bestuzhev-Ryumin was the most extreme republican among the Decembrists; he insisted on the need to execute the Emperor and his entire family. At least four other members of the Bestuzhev family were involved in the Decembrist conspiracy.