While service as a mercenary abroad had relatively neutral connotations in the period,[4] many Scots disliked serving in the Irish Brigade regiments, making recruitment difficult.

[5] A report written by the British agent "A.M." or "Pickle the Spy", now thought to have been Alastair Ruadh MacDonnell of Glengarry, claimed that Sir Hector Maclean was originally intended to be Lieutenant-Colonel, but Drummond "got a stop to [his] obtaining the Commission".

Drummond, the Royal Scots, the Irish Brigade picquets and a number of other French advisors and specialists were embarked at Dunkirk in late November 1745 to support the Jacobite Rising of 1745.

On 2 December, Drummond issued a Declaration stating that they were "come to this Kingdom, with Written Orders, to make War against the King of England, Elector of Hanover, and all his Adherants";[8] he took over from Strathallan as the Jacobite Commander-in-Chief in Scotland, in control of a force of around 3,000.

A message from Drummond confirming his arrival and promising further French reinforcement to come seemed to strengthen the argument for consolidating their position in Scotland, and on 5 December the Jacobite 'Council of War' decided to return there.

[9] Johnstone added that Drummond's report that ten thousand additional French soldiers were expected to follow was "inexcusable", as "this false information [...] greatly influenced us".

[9] Despite Charles's orders that he march to England and join the main field army there, Drummond insisted that the Jacobite forces meet in the central Lowlands, citing French instructions that government-held fortresses should be reduced first.

As a long-term exile he was occasionally insensitive to Scottish customs:[15] when retreating through Aberdeen after Stirling, Drummond was said to have suggested hanging some Church of Scotland ministers "for examples".

[18] Following the defeat at Culloden Drummond escaped Scotland on a French ship with several other senior officers, including his brother: James died on 13 May and was buried at sea.