Chaadayev was born and died in Moscow. His surname is probably derived from the Turkic word Chaadai., with the name deriving from Chagatay, the second son of Genghis Khan. After leaving Moscow University without completing his course in 1812, he entered the army and served in the Napoleonic Wars. Chaadaev's first hand observation of Tsar Alexander's reaction to a revolt in the Semenovsky regiment may have led to his resignation from service in 1820. From 1823 to 1826 he travelled in Europe, so that he was out of Russia during the Decembrist insurrection, though he was questioned on his return about his connections with many of the Decembrists. These connections may have contributed to his failure to find a position in the new government of Nicholas I.