During the 1715 Jacobite Uprising, Lyon served as a recruiter for the rebel forces at Perth. A letter dated 24 October 1715 from Lyon to his brother-in-law, James Carnegie of Finhaven, demonstrates the coercive measures used to secure support. In the correspondence, Lyon warns Carnegie that his reluctance to join the camp at Perth had "enraged" their associates and that his house Milton of Finavon House and estate at Finhaven would be "burnt" and ruined unless he joined the uprising immediately. This letter was later used as evidence in Carnegie's 1716 treason trial at Carlisle to argue that his participation in the rebellion was a result of duress.[1]
After the uprising, Lyon’s widow, Margaret Carnegie (Lady Auchterhouse), provided a sworn statement in August 1716 that shed light on the deep political rift between the two men. She described a "tenacious debate" at Finhaven just before the rebellion, where her brother, James Carnegie, had "argued very warmly for the Revolution and the power of parliament." According to Margaret, Lyon was so troubled by these views that he later remarked he "was sorry to see Finhaven of such principles." This testimony, combined with Lyon’s earlier letters threatening to burn Carnegie’s house and lands, proved critical in Carnegie’s 1716 treason trial, helping to establish that his eventual participation in the rebellion was a result of Lyon's coercion rather than political conviction."Deposition of Margaret Carnegie, Lady Auchterhouse". The National Archives, Kew. State Papers Domestic, George I (SP 35/6/47). Retrieved 16 April 2026.
