The original parish church dates back to the eleventh century, possibly around 1010, the later Benedictine nunnery, built immediately alongside and to the left, and giving rise to an unusual double nave, dates to around 1204, and still later embellishments to the fifteenth, sixteenth and seventeenth centuries.
The church was undamaged by the Great Fire of 1666, although nonetheless requiring to be restored in 1893, only to be damaged by IRA bombs in 1992 and 1993, and restored again in 1993-95.
It is dubbed “The Westminster Abbey of the City” because of the beauty of its interior. The alabaster effigies of Sir John de Oteswich and his wife, salvaged from the church of St Martin Outwich, date to the late fourteenth or early fifteenth century, and numerous other monuments to the fifteenth to seventeenth, including that of Sir John Crosby (d. 1476), Sir Thomas Gresham (d. 1579), and Martin Bond (d. 1643), in his military uniform.
The exterior is substantially surviving thirteenth- to sixteenth- century.
Helen was the mother of the first Christian Roman Emperor, Constantine.