Trained in law, Forbes entered local politics and in 1715 aided the Hanoverian cause during the unsuccessful Jacobite rebellion of that year. Forbes was elected to Parliament in 1722, and in 1737 he became lord president of the Court of Session. When Charles Edward (Charles Edward, the Young Pretender), the Young Pretender, the Stuart claimant to the British throne, invaded Scotland in 1745, Forbes kept Inverness loyal to George II and persuaded the chiefs of two powerful clans—the Macdonalds and the Macleods—not to take the field for the Jacobites. From September 1745 until the suppression of the insurrection in April 1746, Forbes was the main representative of the government in northern Scotland. Nevertheless, he later fell into disfavour with the English for his efforts to mitigate the punishment of the rebels.