In November 1945, long before work had started on the new Cathedral, the West Crypt of the ruined Cathedral which had escaped destruction was dedicated to the principle of a Chapel of Unity binding the Church of England and the Free Churches together for Christian service. This was born out of the sufferings of war and the ecumenical enthusiasm of church leaders.

The building of the new Cathedral offered an opportunity to create a purpose-built Chapel of Unity. It is separate from but linked to the main body of the Cathedral. The form conceived by the architect Sir Basil Spence was that of a tent, the temporary home of a people always ready to move onwards. The exterior walls were clad with green Westmorland Slate, which contrasted pleasantly with the pink sandstone of the Cathedral.

The Chapel of Unity is a separately administered, ecumenical chapel for use by many denominations of the Christian faith. When the Cathedral was consecrated in 1962, this idea was truly innovative.

Every year on 6 August, to commemorate the bombing of Hiroshima and Nagasaki, an event is held with readings and music to remember those who died and to commit to the creation of a world without nuclear weapons. This event is open to the general public and people of all faiths and of none.