In 1860, during the Second Opium War, Zaiyuan and Muyin (穆蔭) travelled to Tongzhou to replace Guiliang (桂良) in the peace negotiations with British and French officials.
When the negotiations failed, the Mongol general Sengge Rinchen took members of the British delegation, including Harry Smith Parkes, Henry Loch, Thomas William Bowlby (a journalist for The Times), and their escorts hostage.
On 18 October, in retaliation for the capture and deaths of the peace delegation, British and French forces sacked and burnt the Old Summer Palace.
Prince Gong, who was ordered to remain behind to make peace with the invaders, successfully concluded the Convention of Beijing with British, French and Russian officials.
Later that year, Prince Gong, with support from the Empress Dowagers Ci'an and Cixi, launched the Xinyou Coup and seized power from the eight regents.