As a diplomat, Crichton took the letters of James VI of Scotland to Henry IV of France and Henri, Duke of Rohan at the siege of Amiens in 1597, and then travelled to Italy. Sanquhar later told a Venetian diplomat in London, Giovanni Carlo Scaramelli, that he had met the Pope in Ferrara. He said he told the Pope that James VI would tolerate Catholics in England at the Union of the Crowns.