He died about the beginning of the year 541, but some days after the Epiphany. Out of devotion to St Benignus, he desired to be buried near that saint's tomb at Dijon; this was executed by his virtuous son Tetricus, who succeeded him in his bishopric.

In dying, Newman sought to enter the world of St Gregory and St Benignus. He wanted to be buried ad sanctos. He believed that nobody became a saint on their own. He believed not only that Father Ambrose St John was a saint, but that he had become a saint and given his life through the stress of overwork, in translating from the German Father Fessler's account of the First Vatican Council of 1870.

 Father Ambrose St John had thereby enabled Newman to build a formidably effective explanation of what Papal Infallibility actually meant. In the inflamed atmosphere of polemic about "Roman Claims" triggered by the First Vatican Council, Newman's Letter to the Duke of Norfolk (1874) persuaded English public opinion that there was no just occasion to launch a kulturkampf against Catholics. Newman had allayed fears and suspicions rooted in centuries of bitter mutual recrimination between Protestants and Catholics.

Burial ad sanctos: Father Ambrose St John was not alone in putting his health at risk in a work for the Church which only Newman could complete. Father Joseph Gordon had suffered likewise and died young, in 1853, from travels which had undermined his health. Under intense strain during the years 1851-1853, he had performed vital and  necessary work in gaining evidence against the false witness of an Italian  priest in England, Father Achilli, who had engaged, while in Italy, in the sexual abuse of innocent women, and was now, in England, engaged in a public assault on the "Church of the Inquisition". 

Newman had publicly unmasked Father Achilli, who fought back with a libel action. There followed a trial and a struggle for the truth which involved the credibility of the Catholic priesthood. It ended in a nominal fine for Newman, and in his public vindication, which was, correspondingly, a vindication of the Catholic priesthood. Between 1850 and 1853, Newman, at the cost of great personal suffering, had helped to protect the Catholic Church in England from a potentially destructive resurgence of anti-Popery. Nobody else could have succeeded.

Newman, however, remained deeply aware that his success was dependent on the help of his Birmingham Oratory confrères. In 1864, he proclaimed his debt in the moving conclusion to his Apologia Pro Vita Sua. In this book, he had once more defended the credibility of the Catholic priesthood. Thanks to Newman, it was becoming harder to regard Catholics as traitors to the nation. The cost, however, was registered in the sickness and death of Father Ambrose St John.