Standing about a mile from the centre of the present town, only the chancel of the once larger medieval church remains. The earliest section may have been built before the church was given to Lanercost Priory in 1169, this part extended eastward in the late-12thc./early-13thc. By the late-17thc. it had already been proposed that a church might be erected in the town, itself, and in 1702/1704 the bishop of Carlisle wrote that the church was in a bad state. In 1788/9, most of the old church was torn down, with the exception of the chancel, which then became a mortuary chapel. The new parish church was created by enlarging the hospital (almshouses) chapel, which was in the centre of the town. A west porch was added to the old chancel in 1861, and further repairs were carried out in the 1890s and in 1987. In 1978, the old church was made redundant. A few medieval grave covers also survive.

Domesday Book did not cover this part of England. Excavations and various documents show that the site where the Old Church is located had once been a Roman Fort. St Martin's Church was built into the NE corner of this enclosure. Brampton was in the area owned by Gilles son of Beth in the 1st half of the 12thc., the area later becoming the Barony of Gilsland. In 1157, Gilsland fell into the king’s hand and Henry II gave it to Hubert de Vallibus (d. 1165). Hubert’s son Robert founded Lanercost Priory in 1169 and gave to it the church at Brampton. Nothing is known about the church prior to it being appropriated to Lanercost Priory by Robert de Vaux. The vicars of Brampton were thereafter appointed by the priory until the Reformation. Osbertus persona de Brampton was one of the witnesses of the Foundation Charter of the Priory of Lanercost of about 1169. The second vicar whose name is known was Thomas, who was instituted in 1220 by Hugh bishop of Carlisle. After the suppression of the priory the advowson was held for several generations by the Dacres of Lanercost. After this line died out it passed to Lord Carlisle.

Robinson has examined the stonework and concluded that the S window above the grave recess is in its original position, but that the grave recess was rebuilt (using original stones) in 1788. He has proposed that the date for the grave recess arch is the same as the eastern extension to the chancel. Robinson's analysis of the S wall shows a number of building and restorations carried out over several centuries. Hyde and Pevsner have suggested that the eastern half of the chancel was added in the late-12c. or early-13thc., an area which includes the piscina and aumbry. The W wall may date from the destruction of the rest of the church in 1788, but the E wall seems likely to have been rebuilt in 1861. Norwood (1889) suggested that the priest’s grave cover under the S exterior arch is 13c. and noted that the window in the walling above it is Norman. Ryder agrees that the grave cover under the arch is likely to date from the 13thc.

There has over the years been some discussion about why the church is located so far from the centre of town, some believing that the town must have been moved to its present site sometime after the church was built. Others, including Collingwood, have refuted this theory. Excavations show that the church was built on the site of a Roman fort. Robinson and a few others suggest that this area had at an early date (post-Roman) been established as a religious site, which might account for the positioning of the Old Church. Neither theory, however, is supported by specific evidence at the moment, so the question concerning the early relationship between the old church and town remains open.