On the west wall, just adjacent to the entrance ramp leading down from the narthex is an ancient grave slab which is believed to date from the second half of the twelfth century.
It is an almost complete slab displaying an incised processional cross, standing on what is probably intended to represent a plinth with three steps leading up to the cross. Beside the cross is a crude representation of a sword, which, we are told, means that this was probably the grave slab of someone of knightly or noble rank. Unfortunately there is no inscription of any form, so we have no way of knowing just whose grave the slab covered.
Close to this grave slab, on the north wall of the church is a much smaller and broken grave slab, with a crudely incised cross and sword upon it, apparently of a similar period and age to the first.
Further along the north wall of the church is another incised stone with what looks to many people like a representation of an axe upon it. This represents, not an axe, but a stone mason’s gauge or square, to aid in the accurate measurement and drawing of the angles necessary to effect the work in the building of parts of the Church.
It has been speculated that it may have been intended to form the grave slab of a mason who died while engaged in work on the Church. Apparently, it is the only one of its kind in Scotland.
At various points along the north and south walls of the nave are small alcoves containing fragments of the architecture of the original Norman church of Bothwell which was founded in the middle years of the twelfth century
Also of interest is the fourteenth century chancel, founded by Archibald Douglas, “Archibald the Grim”, as a Collegiate Church in 1398, which has two interesting heraldic tombs of the First and Second Earls of Forfar at the east end, with the ornate tomb monument of William Douglas, Third Duke of Hamilton, along the north wall of the chancel. It dates from 1696, and was brought from the old Collegiate Church of Hamilton, when the ruins of that building were demolished in 1852.
On the north wall of the chancel, just next to the Duke of Hamilton’s monument, is the door to what was the sacristy of the old Collegiate Church, but is now the vestry of the modern Church. It has interesting ribbed vaulting, and on its southern wall, is a piscina.
On the south wall of the chancel, is a piscina for washing the sacred vessels after the communion service, and further along the south wall from them are the sedilia. These were the seats where the celebrant priests of the old Collegiate Church sat in order of rank, during the celebration of the Mass.
On the south side of the Chancel also is to be seen the only surviving medieval door in the Church, known as the “Priests’ Door”.
Re-entering the nave, one sees a number of fragments of medieval masonry from the old Norman Church built into the walls or placed in small alcoves. One of the most interesting is what looks like a lintel of a doorway inscribed in Gothic lettering with the words “Magister Thomas Trayl”. This dates from the opening years of the fifteenth century and Thomas Trayl, who was a brother of Walter Trayl, Bishop of St. Andrews(1385-1401).
On the south- western wall of the Church also is an interesting and very large fragment of a grave slab of someone who either was a member of the de Moray family who built the earliest surviving parts of Bothwell Castle, or who may have been one of their knightly retainers. Incised on it is a knightly sword, together with a shield bearing the de Moray arms of three mullets.
Bothwell Parish Church also has some noteworthy stained glass. In the Western Wall is some fine Victorian Stained Glass.