The organ of Grace Church on-the-Hill is a three-manual and pedal instrument by Casavant Freres, 1926. The instrument was a gift to Grace Church from Robert Charles Matthews, P.C. Casavant made additions and tonal revisions in 1960.

In 1979, Richard Valentine Porritt made a generous donation to the Church for repairs to the organ, or its replacement. By 1997, when the Church was about to undergo a major renaissance, it was determined that the organ console required replacement. This project was completed by R. A. Denton of Hamilton, Ontario, thanks to the generosity of the Porritt family.

Extensive repairs, additions, and tonal re-visions deemed necessary in 2004-5. This rebuilding of the organ was a gift given ot the glory of God and in thanksgiving for the lives of Ruth and John McCarthy, and dedicated on November 20, 2005. The work was done by Andrew Mead of Mead Musical Services.Tonal design and voicing was done by Thomas A. Fitches.