Sts. Peter and Paulís Old Cathedral is constructed from a locally quarried greenstone called diorite porphyrite, an igneous rock.  All the sandstone used in the construction of the Cathedral was quarried locally from the Marulan area.  The roof slates were imported from Bangor. 

Construction of the Cathedral commenced in 1871 and was completed in 1890. 

The Bell, which had come from Ireland in 1869, was placed on a wooden tower between the old brick church and the presbytery.  The bell was rehung in the new tower in April, 1890, when the second stage of the Cathedral was completed.

All windows, jambs, window sills, arches, coping, triangle caps, buttress caps, quoins and base are made of Wingello stone, from the Marulan areas.

The woodwork in the ceiling throughout is of special interest, panelled with exposed rafters, purlins and principal beam in the nave aisles.  In the nave there are exposed purlin beams and bracketed principal beams, which also appear in the transept and Sanctuary.  The fretwork detail on the brackets under the principal roof beams are a distinct feature of the ceiling.

The pillars inside the Cathedral are of Malmsbury bluestone.  Unfortunately the columns were painted and sanded to look like sandstone in the 1927/28 renovation.  One of the objectives of the restoration is to restore the columns to their original state.

The windows in the Cathedral are particularly fine.  The smaller windows at the back of the nave on the northern and southern sides are of enamelled glass.  Some of the windows installed during the second stage were made by Grosse de Herde, a Belgium company, and are quite distinctive.  All the clerestory windows are by Grosse de Herde  A large window depicting the Transfiguration of Jesus in the southern transept were donated by Bishop Lanigan.

The window above the altar on the eastern front was donated by Mrs. Dalglish and was by John Hardman and Company.  Research is currently being undertaken regarding the design and construction of the window in the western wall.

The sanctuary area was renovated extensively during the 1927/28 work.  The main altar was moved back against the eastern wall and the sanctuary floor was raised.  The sanctuary area was lined with marble.

There are several brass works based on designs by British Architects August Welby Pugin and his son, Edward Welby Pugin. These pieces have been repaired, cleaned and restored.

There were two murals on the eastern wall each side of the main altar but these were painted over.  An attempt has been made to see if it is possible to restore them but they were sanded over prior to painting.

The floor in the Cathedral is a swung concrete floor (constructed in 1927/28 to avoid the damp problem) which was then covered with wooden parquetry.  Rubber tiles on a bitumen base were put down in 1957.  Part of our current project is to remove the tiles and restore the parquetry, if possible.