His mother Frances was the second daughter of William Herbert, Marquess of Powis, one of the five Catholic lords falsely accused of conspiring to assassinate Charles II in the Popish Plot.

His father went into exile following the 1688 Glorious Revolution and took part in the 1690 Jacobite campaign in Scotland but surrendered to the new government in 1691; he spent most of the next ten years in and out of prison and died in 1701, leaving huge financial debts; his widow sent William and a daughter to France to be educated and brought up as Catholics.

The Duchess of Seaforth was the daughter and heiress of Nicholas Kennett of Coxhoe, county Durham, and educated in France under Jesuits.

[5] After the battle, he was nominated by the Chevalier lieutenant-general and commander of the northern counties, and went north to endeavour to recover Inverness, which had been captured for the government by Simon Fraser, lord Lovat.

Although joined by Alexander Gordon, marquis of Huntly, he was unable to raise forces sufficient to make way against the Earl of Sutherland, and gave in their submission.

Shortly afterwards, Seaforth crossed over to the Isle of Lewis, where he endeavoured to collect a number of his followers; but when a detachment of government troops had been sent against him, he escaped to Ross-shire, whence he set sail for France, reaching St. Germains in February 1716.

He was severely wounded at the battle of Glenshiel on 10 June, but was carried on board a vessel by his followers, and, escaping to the Western Isles, returned thence to France.

After the passing of the disarming act in 1725 they, however, agreed on his private recommendation to give up their arms, and in future to pay rent to the government on condition that they were discharged of all arrears.