A medieval cross, possibly Romanesque, hangs on the W interior wall of the S vestibule, near the entrance porch of the church. The cross is carved in relief, with four equally-shaped arms. From the bottom edge of the lower arm a staff emerges, this carved centrally along the length of the stone. According to the Rev. David Gordon (New Statistical Accounts, 1845) a stone 'on which is a figure bearing a near resemblance to a Maltese cross' was 'taken from a grave'. In 1855, Thomas Muir published a drawing of it in his Notes on Remains of Eccleiastical Architecture and Scuptured Memorials. The inventory of the Royal Commission Ancient and Historical Monuments of Scotland (1915) records that 'a slab of red sandstone having a cross of Maltese form carved upon it in low relief ... was found in the east wall of the old parish church when taken down some twenty years ago'. In the late 17th century it was mentioned that the church was in need of substantial repairs. It was eventually rebuilt in 1736, enlarged in 1834, and rebuilt again in 1891-2. Nothing of the present church structure is medieval.

Earlston is generally called Ercheldune, Ercheldon, Erceldoun, Erchildon and Ersledun in medieval texts. A royal charter to the Abbey of Melrose in 1143/44 was signed at Earlston, and the church there was mentioned when Walter de Lyndesey granted it to the Abbey of Kelso, probably about 1160. This was opposed by the monks of Durham, who claimed that it was already theirs. They argued that the then chapel of Earlston had been given to Edrom, which had itself been given to the monks of Durham sometime between 1124 and 1138. Edrom came under the holdings of the Priory of Coldingham, which was a cell of Durham. John, abbot of Kelso, along with Lawrence, abbot of Melrose, acted as papal judges during the despute (1175 X 1178). Following this, Richard, bishop of St Andrews, confirmed to the monks of Durham their possession of Earlston's church (1172 X 1177), as did Pope Alexander III (1162 X 1181). In 1186, Pope Urban III listed Earlston, among other churches, as a possession of the church of Durham. Patrick I Earl of Dunbar confirmed the churches of Edrom, Earlston and other places to Durham in about 1189-98, and Bertram, prior of Durham (1189X1209 or 1213), granted a concession from the altarage of Earlston to the nephew of the Prior of Coldingham as vicar of Earlston. It may have been at this time that Earlston was given full parochial status with a perpetual vicarage. David de Bernham, bishop of St Andrews, dedicated/consecrated the church of Earlston in 1243, following papal orders about the consecration of churches. In the Bagimond Roll of the 1270s, Earlston was listed as 'Vicarius de Erceldoun'. Repairs, leading to some re-building, were undertaken on the chancel of the church in the 14th century. It remained annexed to the Priory of Coldingham until the Reformation.

The re-use of medieval stones carved with crosses in later church fabrics, some of which may have been parts of grave covers, is not unique to Earlston. A similar cross, for example, can be found built into the N exterior of Duddingston Church (Midlothian).

The dating of the cross at Earlston must inevitably be based on stylistic comparisons. The general type found at Earlston, with triangular-like arms meeting in a central circular area is not uncommon during the Romanesque period. An interesting comparison can be made with the Romanesque cross carved on a grave cover formerly in Lincoln Cathedral. Both the Earlston and Lincoln crosses have the additional feature of a wider section at the top of the shaft, just under the cross. (For an image of the Lincoln Cathedral grave cover, see: E. Cutts, A Manual for the Study of The Sepulchral Slabs and Crosses of the Middle Ages, London, 1849, pl. XLI.)

The source for the 1915 Royal Commission of Scotland's report that the stone with cross had been found in the east wall of the previous wall is uncertain. If this statement is correct, then the cross must have been visible in the earlier church in order for it to have been mentioned in 1845 and a drawing of it published in 1855.

Coldingham Priory was founded in the late 1090s as a cell of Durham Cathedral Priory. Documents sometimes refer to churches as owned by Durham even when, in fact, they were actually directly dependent on Coldingham Priory. Ultimately, of course, the mother house was Durham but it is not always made clear in the early years when the immediate governance was via Coldingham. Did the relevant Scottish churches always refer directly to the monks of Coldingham, or did the monks of Durham sometimes have the more immediate control?