In May, along with his cousin and fellow priest, eighty year old Fr John Kemble, Fr Lewis was taken to London. Here he was examined by Titus Oates and other anti-Catholics including Lord Shaftesbury. Lord Shaftesbury offered the priest his life and rich rewards if he would tell them about the plot or conform to the Protestant religion. The good priest said he was unable to tell anything about the plot because he knew of no plot. Neither would he conform because, he said, it was against his conscience. He was sent back to Usk to await execution.
Three months later, on 27th August 1679, the condemned priest was taken from the Gaol on Bridge Street. He was tied to a hurdle, feet foremost, and drawn along the river path to the place of execution. This was in the grounds of what is now Porth-y-Carne House. (Less than a week earlier, on 22nd August, the aged Fr John Kemble had been martyred at Hereford.) In the 1800s, a Catholic Church, dedicated to St Francis Xavier, was built opposite the site of the martyrdom of St David Lewis. Fr David Lewis was canonised by Pope Paul VI on 25th October 1970. In 1974, the Church of St Francis Xavier was rededicated and, in honour of the martyred priest, it is now known as the Church of St David Lewis and St Francis Xavier.