The Cathedral Church of Christ, also called the Cathedral of the Universities Mission in Central Africa (UMCA), is near the junction of Creek Road and Sultan Ahmed Mugheiri Road (formerly New Mkunazini Road) on the eastern side of Stone Town. It stands on the site of the slave market, used in the 18th and 19th centuries when Zanzibar was a large slaving centre.

A group of UMCA missionaries had originally come to east Africa in 1861, following the call of the explorer David Livingstone to oppose the slave trade and spread Christianity across Africa. In 1864 they settled in Zanzibar, after a number of earlier sites proved unsuccessful. When the slave market was closed by Sultan Barghash in 1873 the missionaries bought the site and almost immediately started building the cathedral. Some adjoining land was donated to the mission by a wealthy Indian merchant called Jairam Senji. Today, nothing of the old slave market remains (but see St Monica's Hostel below).

When the first service was held in the cathedral, on Christmas Day 1877, the roof was not finished. It was finally completed in 1880. Tradition has it that the cathedral's altar stands on the site of a tree to which the slaves were tied and then whipped to show their strength and hardiness. Those who cried out the least during the whipping were considered the strongest, and sold for higher prices.

The man who was the force and inspiration behind the building of the cathedral was Bishop Edward Steere, who was Bishop of Zanzibar from 1874 to 1882. (He was also the first compiler of an English–Swahili dictionary, using the Roman alphabet; until then Swahili had been written using Arabic script.) He trained local people as masons and used coral stone and cement for building materials. Sultan Barghash is reputed to have asked Bishop Steere not to build the cathedral tower higher than the House of Wonders. When the bishop agreed, the sultan presented the cathedral with its clock. The tower was finished in 1883.

The legacy of David Livingstone lives on in the cathedral: a window is dedicated to his memory, and the church's crucifix is made from the tree that marked the place where his heart was buried at the village of Chitambo, Zambia.

The mosaic decorations on the altar were given to the cathedral by Miss Caroline Thackeray (a cousin of the English novelist William Makepeace Thackeray), who was a teacher at the mission here from 1877 to 1902.

Behind the altar is the bishop's throne and 12 other seats for the canons. They are decorated with copper panels and show the names of several biblical figures, written in Swahili. The window behind the altar has been decorated with pictures of African saints, from Egypt, Carthage and Ethiopia.

Around the church are many plaques, dedicated to the memory of missionaries who died here, and to the sailors and airmen who were killed in action during the East Africa Campaign of World War I.

Today, services are held every Sunday (in Swahili), and an English service is held on the first Sunday of the month. The cathedral is also open to visitors.

Outside the cathedral, in a small garden next to the school, is a sculpture of four slaves chained in a pit – an understated yet powerfully emotive work of art that is well worth seeing.

During the day (except at service times) there is an entry fee of US$10, payable at a small kiosk, to the cathedral and surrounding area (which includes the slave sculpture).