Southwark's Catholic cathedral was destroyed by in a 1941 bombing raid and so one of his immediate pastoral priorities was to re-construct the cathedral. He attended all of the sessions of the
Second Vatican Council. On 28 May 1965, aged 60, he was appointed as the first metropolitan
Archbishop of Southwark by
Pope Paul VI. On the same date a new diocese
Roman Catholic Diocese of Arundel and Brighton was created by carving out a large southern portion of his diocese. Recently-revealed archives show that in 1957 Cowderoy took a hardline approach from a Dutch priest and future Vatican Cardinal
Johannes Willebrands to come and speak on
ecumenism in his diocese: "I do not agree with it and I do not like it...if the Holy See leaves me to judge, I would say no". In 1968, he took a hard line on the controversial
papal encyclical Humanae Vitae and disciplined a young priest in his diocese and called the document on artificial birth control "regrettable". Cowderoy's position was in contrast to the more moderate approsach of his fellow London Archbishop,
John Heenan. He was Grand Prior for England and Wales of the Knights of the
Order of the Holy Sepulchre of Jerusalem. He died suddenly on 10 October 1976, aged 71, shortly after celebrating mass. ==Consecrator==