Westminster Abbey stopped serving as a monastery in 1559, at roughly the same time it became an Anglican church (part of the Church of England) and formally left the Catholic hierarchy. In 1560, the church was granted “Royal Peculiar” status.

Westminster Abbey is not Catholic because it is a Royal Peculiar and part of the Church of England (Anglican), the state church established by King Henry VIII during the English Reformation in the 16th century. Historically, the Abbey was a Catholic Benedictine monastery until 1539, when Henry VIII dissolved the monasteries as part of his break from the Pope in Rome. While it was briefly restored to the Catholic Church under Queen Mary I, it returned to the Church of England under Queen Elizabeth I in 1560 and has remained so ever since. As a "Royal Peculiar," the Abbey is not subject to a bishop or an archbishop but is directly under the jurisdiction of the British Monarch. This unique status allows it to serve as the nation's "coronation church" and a place of burial for monarchs and significant cultural figures. While it may look architecturally like a Catholic cathedral and retains many liturgical traditions that feel "Catholic" (high church Anglicanism), it is fundamentally a Protestant institution that remains the symbolic heart of the British Monarchy and the Anglican faith, reflecting the unique religious and political history of the United Kingdom.