1892
Archbishop Reynolds has two stained glass windows erected in memory of the second and third bishops, Geoghegan and Sheil. They are made by the Adelaide firm of Montgomerey and Grimbly.

1893
June 12, Archbishop Reynolds dies aged 59. He is buried at Cabra Convent.

1895
January 5, Archbishop John O'Reily (previously consecrated Bishop of Port Augusta on 1 May 1888) is appointed Archbishop of Adelaide. Archbishop O'Reily has the task of raising funds to pay back a huge debt incurred by his predecessor.

O'Reily is highly regarded in Australia as a pioneer of the reform of

Cathedral sanctuary pre Vatican II

Church music according to the instructions of Pope St Pius X of 1903.

1904
Electric light is installed.

1914
16 August Archbishop Robert Spence, a Dominican, is consecrated as Coadjutor Archbishop of Adelaide.

1915
July 6, Archbishop O'Reily dies.

16 August, Archbishop Spence becomes Archbishop of Adelaide. Like his predecessor he continues to work to clear the diocesan debt. He is able to see the final section of the cathedral opened in 1926. The tower is still to be completed.

1917
April, The Southern Cross records the blessing of statues of the Sacred Heart and St Francis Xavier and St Patrick at the cathedral. When first was placed inside the cathedral, the statue of St Francis Xavier is housed in the St Francis Xavier chapel. Its surrounding woodcarving now forms the surround for the tabernacle. The original base of the statue will later be used for the legs for the high altar.

1921
24 June, a gold chalice is presented by the Catholics of Adelaide to the Archbishop on his return from his ad limina visit to Rome .

1923
21 October, the foundation stone for the northern and western sections of the cathedral is laid.

1926
The major extensions are opened on 18 April. They include all the work north of the fifth column from the altar, the whole of the western section, the porch, the gallery, the new pipe organ and the truncated tower. The architect is Walter Bagot.

The baptistery lies at the base of the tower. Both the font and the statue of St John the Baptist were carved in 1925 from marble by the Luigi Tommasi studio in Tuscany. They are given by Count Thomas J O'Loughlin of Melbourne, as are the gates and railings of the baptistery (formerly from a fence at St Peter's Cathedral) and the windows of the façade of the building. The font is Gothic in style. On seven sides of the bowl are carved acanthus-leaf designs. On the eighth side is a scene of the Baptism of Christ.

Apart from the tower, the present façade is that of 1926.