He was Louis XVI's last minister of war (July 1792), and organized the defence of the Tuileries for August 10. Commanded by the Legislative Assembly to send away the Swiss guards, he refused, and was arrested for treason to the nation and sent to Orleans to be tried.
At the end of August the Assembly ordered Abancourt and the other prisoners at Orleans to be transferred to Paris with an escort commanded by Claude Fournier, the American. At Versailles they learned of the massacres at Paris, and Abancourt and his fellow-prisoners were murdered in cold blood on September 8, 1792. Fournier was unjustly charged with complicity in the crime.