The High Altar is a slab of hard stone, supported by columns of local stone with moulded bases and carved caps of Mount Somers stone. It was a gift of Dr James Irving as a thanks-offering for a safe voyage from England 1879.
Behind the High Altar is the magnificent reredos, erected in 1950 to the design of R.S.D. Harman, who worked closely with Bishop (then Dean) Warren. It was executed by Messrs Gurnsey and Vivian from the kauri decking of an old bridge over the Hurunui. The four bosses hanging down portray the instruments of the Passion of Christ. The six carved figures represent men who established the Anglican Church in New Zealand. The first on the left is that of Samuel Marsden, the middle figure on the left being that of Archdeacon Henry Williams, and the lowest figure that of Tamihana te Rauparaha, son of a famous warrior chief and a Maori leader who was baptised by Bishop Selwyn in 1843 and in the same year accompanied another Christian Maori to the South Island to bring the message of Christianity. The figures on the right hand side are those of Bishop Selwyn, Bishop Harper (who holds a model of the Cathedral in his left hand), and Bishop Patteson. On either side of the altar, the carved oak panelling is surmounted by the Arms of the dioceses of New Zealand. To the left of the altar, the episcopal chair and surrounding panel can be seen. This chair, the desk, and surrounding panelling, were placed in the sanctuary in memory of Campbell West-Watson, CMG, DD, Bishop of Christchurch 1926-51, Primate and Archbishop of New Zealand 1940-51, Foundation Chairman of the National Council of Churches in New Zealand 1941-45. On the back of the episcopal chair are carved the names of the successive bishops of Christchurch. The dossal, which hangs behind the High Altar, was the Centenary gift of the Canterbury Embroiderers' Guild and was designed by Mr W.A. Sutton. The design suggests the burst of life coming from the empty cross and the lighting has been arranged to create the illusion of the three crosses of Calvary. It is estimated that the embroiderers spent over 1,500 hours making the dossal.
On the opposite side of the chancel is the canopied stall of the Dean of Christchurch, designed by Paul Pascoe and carved by Mr J. Vivian; and in the vicinity are seats of the clergy and an inscribed list of the archdeacons who have served the diocese. The altar rail, of polished wood resting on brass standards with foliated tops, is a memorial to George Frederick Tendall, the second organist of the Cathedral. On the left side of the High Altar will be seen the diocesan banner, bearing symbolically the First Four Ships, in memory of the Canterbury Pilgrims, and on the right side is the Cathedral banner, presented by pioneer families at the time of the centennial in 1950. The figure of Christ dominates the banner which also contains the Arms of the Diocese of Canterbury, of Christ Church Oxford, and the Diocese of Christchurch, New Zealand. Native flowers are embroidered on each side.
The apse windows were designed in accordance with the general scheme of B.W. Mountfort and placed in position in 1906. In the centre light, Christ is enthroned. Immediately under His feet are the cross and a group of angels, while lower still is the figure of St Michael and St Raphael. This is in memory of those Canterbury colonists who arrived prior to 31 March 1853. The north light shows the Virgin Mary sitting surrounded by a choir of angels while below is a group of saints, chief among them being St Peter. This is in memory of John Studholme, Studholme was a student at Queen's College, Oxford at the time Dean Jacobs was a Fellow in residence there. He became interested in the Canterbury Association and arrived in Lyttelton in 1851. He held land in different parts of Canterbury and in 1857 became the first representative of Timaru in the Provincial Council. He was a Member of Parliament 1867-74 and again 1879-81. He married a sister of William Sefton Moorhouse, a Superintendent of Canterbury.
The south light shows St Paul and other saints set under the heavenly choir, leading the universal praise to the glory of Christ. It is in memory of Ellen, wife of John Studholme.