In 1745 he assisted his father set up a volunteer regiment in Rutland to assist in quelling the Jacobite Rebellion of 1745. Although the regiment was limited to garrison duty at Newcastle, it was the only one of its type that raised its full quota of 780 recruits. Manners received a commission as colonel of the regiment. Even though the regiment never got beyond Newcastle, the young Marquess of Granby went to the front as a volunteer on the Duke of Cumberland's staff and saw active service in the last stages of the insurrection, being present at the Battle of Culloden. In Newcastle the regiment mutinied because they had not been paid but Granby paid the money owed out of his own pocket before they were due to be disbanded. Thereafter he left England for Flanders as Intelligence Officer to Cumberland.