The Baptistery was added to St Peter's in 1901 at the cost of £4000. It was designed by Austin and Paley. Its roof is made of copper. It is octagonal in shape, with gates on only one side, leading into the church. This reminds us that baptism is the sacrament that makes us members of the Church.
The font is made of Connemara marble. The Latin inscription around it is a quotation from Romans 6:3: When we were baptised in Christ Jesus, we were baptised in His death.
The stained glass windows in the Baptistery depict various saints, with many images of them baptising. A carving on the altar shows an image of Jesus' own baptism in the river Jordan.