The organ in its present position was built and dedicated in 1876. It was completely rebuilt in 1915 by William Hill & Son, famous for the organs of York Minster, Birmingham Town Hall and Sydney Town Hall. An addition to the Pedal Organ of 'Trombone sixteen feet' was given in 1925.

The organ is built between the two Chancel arches and, together with the Screen, separates the Chancel from the Jesus Chapel. There are two manuals and pedals of twenty speaking stops and three couplers. Its fine tone is much admired by those who enjoy organ music.

In 1997 a very generous donation made it possible for a major restoration to be carried out by Harrison & Harrison of Durham, and at that time the key action was electrified and a 'mixture' added to the Great Organ.

The choir leads the congregation in the singing of hymns, canticles and psalms and also sings two choral works from its substantial repertoire every Sunday .

Music at Saint Mary's also includes performances by visiting groups - from Choral Societies to Brass Band Music. Concerts also include occasional Organ Recitals and are usually in aid of the various charities that Saint Mary's supports.