Prior to the elevation of Ely Cathedral as the seat of the diocese, it existed as first as a convent of religious sisters and later as a monastery.

A new Benedictine monastery was built and endowed on the site by Saint Athelwold, Bishop of Winchester, in 970, in a wave of monastic refoundations which also included Peterborough and Ramsey.

The earliest historical notice of Ely is given by the Venerable Bede who writes (Historia ecclesiastica gentis Anglorum, IV, xix): Ely is in the province of the East Angles, a country of about six hundred families, in the nature of an island, enclosed either with marshes or waters, and therefore it has its name from the great abundance of eels which are taken in those marshes.This district was assigned in 649 to saint Æthelthryth, daughter of Anna, king of the East Angles, as a dowry in her marriage with Tonbert of the South Girvii.

After her second marriage to Ecgfrith of Northumbria, she became a nun, and in 673 returned to Ely and founded a monastery on the site of the present cathedral.

As endowment she gave it her entire principality of the isle, from which subsequent Bishops of Ely derived their temporal power.

For more than a century the monastery flourished, and about the year 1105 Abbot Richard suggested the creation of the See of Ely, to relieve the enormous Diocese of Lincoln.

Since the Reformation, notable bishops have included Lancelot Andrewes, Matthew Wren, Peter Gunning and Simon Patrick who, in 1695 gave the Shambles estate in Wisbech, to provide clothing for the poor.