The fifth and last Earl, was possessed of excellent abilities, but from his early years he displayed a marked eccentricity of character. Some family misunderstandings caused him to leave home while a mere youth, and he spent several years in France as bellows-blower and assistant to a blacksmith, without holding any intercourse with his family. On the death of his father, Viscount Kingston the next heir, taking for granted that the young Earl was dead was proceeding to take possession of the title and estates, when he suddenly appeared and vindicated his rights. It was afterwards ascertained that a confidential servant kept him apprised of what was taking place at home and in the family and had sent him notice of his father’s death.  The Seton family, as we have seen, had always been noted for their loyalty and their attachment to the old Church, and the last Earl, though he had renounced the Romish faith, held firmly to the political creed of his ancestors. He was living peaceably in his own mansion at Seton when the rebellion of 1715 broke out. It is probable that he would, under any circumstances, have taken the field in behalf of the representative of the ancient Scottish sovereigns but his doing so was hastened, if not caused, by the outrageous treatment which he received from a body of the Lothian militia, who forcibly entered and rifled his mansion at Seton.
The Earl fought with great gallantry at the barricades of Preston but was at last obliged to surrender along with the other insurgents and was carried a prisoner to London and confined in the Tower. He was brought to trial before the House of Lords, 15th March, 1716, and defended himself with considerable ingenuity. The High Steward, Lord Cooper, having overruled his objections to the indictment with some harshness, ‘I hope,’ was the Earl’s rejoinder, ‘you will do me justice, and not make use of "Cowper-law," as we used to say in our country—hang a man first and then judge him.’ On the refusal of his entreaty to be heard by counsel, he replied— ‘Since your lordship will not allow me counsel, I don’t know nothing.’ He was of course found guilty, and condemned to be beheaded on Tower Hill. ‘When waiting his fate in the Tower,’ says Sir Walter Scott, ‘he made good use of his mechanical skill, sawing through with great ingenuity the bars of the windows of his prison, through which he made his escape.’ He ended his life in Rome, in 1749, aged seventy, and with him terminated the main branch of the long and illustrious line of the Setons.