In medieval times there appears to have been a peal of five bells at St. Mary’s with a tenor of approximately 22 cwt.  The first mention of bells in the churchwardens’ accounts was in 1550-1553, whilst the Minster was being rebuilt using material from the ruins of Reading Abbey.  Two tenors were sold for £57.3s.3d. to help pay for this work and the three remaining bells re-hung.
During 1558-1559 one of the bells was recast and a year later the tenor was also re-hung.  The tenor received attention again in 1585 when it was recast by William Knight II of Reading.  This ring of three remained untouched until about 1603-1604 when two new bells were added.  The new fourth (cast by Henry Knight I) was mainly paid for by the Vicar, Dr. Powell, with public subscriptions providing the balance.  In 1604, a tenor (cast by Robert Mot at the Whitechapel Foundry) was hung and was a gift from Lady Jemmat Webbe.  This bell was brought to Reading by river and hung under the supervision of one “Olde ffather Barnes”.
A new treble was added in 1617 (details of founder unknown).  This bell weighed 8cwt, 3lbs and was paid for using donations from parishioners.  St. Mary’s now had a ring of six and was one of the first churches in Berkshire to reach this number.
Between 1640 and 1642 at least four of the bells were recast. No more major work took place until 1740, when Robert Catlin of London cast and hung two trebles to form a ring of eight (a tablet on the wall of the ringing chamber indicates this).  These bells (costing £102.7s.10d.) were given by William Strode and John Blagrave, Members of Parliament for Reading.  At the end of the year, on Christmas Eve, the first peal on the bells was rung, being a 5040 of Union Triples.  In 1743, Catlin recast the fifth, sixth and seventh, the first two of which were the last remaining bells of the original pre-1550 five.  The seventh was recast again in 1863 by George Mears and the peal assumed its present form.
Towards the end of the 1920s the bells were becoming difficult to handle and at the end of September 1928 the frame was condemned as unsafe and ringing ceased.  In January 1929, Mears and Stainbanks removed the original oak frame and installed a new iron frame, as well as re-hanging the bells with completely new fittings.  The cannons were removed and the new tenor reduced from its former 28-30cwt to its present 25cwt, 2qtr.261b.  The entire cost of the work (£490) was met by Dr. J. Leonard Joyce, a noted local surgeon and Captain of St. Mary’s Ringers.  The newly renovated bells were dedicated by Bishop Shaw on Tuesday 9th April 1929, the Patronal Festival, and the first ringing took place after Evensong that day.  
A full maintenance of the frame and fittings (including refurbishment of the clappers) was carried out by Whites of Appleton in 2003.  The ringing chamber was also decorated at this time and a new ceiling installed.