He was a strong partisan of King James II, and in 1685 was one of the principal supporters of the act of attainder against the Duke of Monmouth; but he remained in England when William III ascended the throne in the Revolution of 1688.

He had financial problems and in 1688 he sold the rump of the family estates and Wallington Hall to Sir William Blackett for £4,000 and an annuity of £2,000 a year.

After the seizure of his fellow conspirators, Robert Charnock and others, he remained in hiding until the imprudent conduct of his friends in attempting to induce one of the witnesses against him to leave the country led to his arrest in June 1696.

[3] To save himself he offered to reveal all he knew about the Jacobite conspiracies; but his confession was a farce, being confined to charges against some of the leading Whig noblemen, which were damaging, but not conclusive.

His wife, Mary, persevered in her attempts to save his life,[5] but her efforts were fruitless, and Fenwick was beheaded in London on 28 January 1697, with the same formalities as were usually observed at the execution of a peer.