Mitchell became part of the burgeoning first generation of Anglican church workers to join the new Diocese of Bloemfontein, formed under its inaugural bishop, Edward Twells, in 1863. Within a month of his arrival, on 18 December 1864, Mitchell was ordained deacon, in Bloemfontein, and he took up residence at Thaba ‘Nchu on 10 May the following year.
Thaba 'Nchu was at the time the capital of an independent Barolong polity within the Free State, ruled by Kgosi (Chief) Moroka II (it was annexed to the Free State in 1884 following the death of Moroka’s adopted son and successor Tshipinare). In a report of June 1865 Twells recorded that Mitchell was “studying the language” (SeTswana) and “commencing the mission work”. Deacon Mitchell was recalled to Bloemfontein in 1867, to extend work there through the newly established St Patrick's mission.
Mitchell was ordained by Twells to the priesthood on Trinity Sunday 1869 - the first occasion of the ordering of a priest in the diocese – and was sent to assist Canon Beckett of the Brotherhood of St Augustine, who was at Thaba 'Nchu prior to the brotherhood's relocation to Modderpoort. For a time Mitchell ran the mission at Thaba 'Nchu unassisted.
The Revd William Crisp joined the mission at Thaba 'Nchu, where Mitchell continued until 1880 – save for a period when he visited England.
In 1880 Mitchell was appointed to a new mission at Kimberley, then still part of the Diocese of Bloemfontein, where he served the mining compounds and co-founded the parish of St Matthew's, Barkly Road. He remained in Kimberley in his retirement and was still active as a priest in what was by then the Diocese of Kimberley and Kuruman in 1913.
St Matthew's was founded jointly by Mitchell and Canon W.H.R. Bevan. In 1882 Mitchell secured the land on which the church was to be built. It was erected in 1888 and dedicated by the Bishop of Bloemfontein on 2 June 1889.[4]
