In 1673, when he was aged 24, he entered the French Army of Louis XIV and served under the famous Marshal de Turenne before returning to Scotland sometime around 1675.

The Duke owed these positions to his Catholicism, Around this time, he was described as being "a libertine and a fop, he is a Roman Catholic because he was bred so, but otherwise thinks very little of revealed religion.

As a result of his actions in Edinburgh, he was received somewhat coldly by King James at his residence in exile, the Château de Saint-Germain-en-Laye, near Paris.

The Duke temporarily regained favour with the accession of Queen Anne in 1702 and was recognised by her as a Knight of the Thistle when she revived the Order on 31 December 1703.

The historian Macky, in his book Characters, observed the Duke and said that "he hath a great many links, but they do not make a complete chain; is certainly a very fine gentleman and understands conversation and the belles lettres; is well bred.