In 1808, in a private capacity, Vaughan accompanied Charles Stuart to Spain, and was present at the assembly of the northern juntas at Lugo; thence he went to Madrid, and travelled to Saragossa with Colonel Charles Doyle. On his return to Madrid, he was sent with dispatches relating to the Battle of Tudela to Sir John Moore at Salamanca, and returned to England in December 1808. In 1809, he published his "Narrative of the Siege of Zaragoza", which reached a fifth edition within the year.