St Mary and St Peter's is noted in particular for its association with and memorials to the Harlaxton Manor Gregory and de Ligne families, c.1410 effigies of Sir Richard Rickhill and his wife, Elizabeth, and the church's 19th-century restoration by John Oldrid Scott The church is within the Harlaxton conservation area.

[7][16] At some point, and by a person unknown, one and a half acres of land (called a 'close'), was endowed to the rector for the ringing of the sanctus bell at 4am and 8pm each day.

[14] In 1855 the parish incumbent was Rev Henry Mirehouse MA, who held a living and rectory of a yearly value of £550 and about 200 acres (0.8 km2) of glebe land under the patronage of the prebendary of South Grantham.

[1] An archeological Watching Brief was held in 2005 during trench groundwork at the south, west and north of the church to establish pipes for a new heating system.

During the work evidence of earlier building was not discovered but a stone fragment was uncovered together with a number of small bones and a skull.

The spire is topped by a finial with weathercock, and at its lower part contains a single run of twin-light pointed arch lucarnes, these on each alternate face, each set-in gables with a globed device attached above.

The tower first stage contains one large pointed arch Decorated window, this on the west side, with no hood mould and plain glazed with twin lights (lancets) leading to trefoil heads.

The tower sits on a simple moulded socle (plinth) topped by a cill band—angled projection that allows water to flow from a building face—which continues around the whole church apart from the south aisle.

The clerestory contains vertically segmented clear glazed twin-light windows, four each north and south, all containing panel tracery—a Perpendicular style of upright straight openings above lower lights—within flattened arches with hood moulds with label stops.

The early 15th-century north aisle is of string-coursed ashlar, buttressed, with four windows of same appearance and style—rectilinear with inset three lights of simple round head, diamond-pattern leaded clear glazing, and flattened hood moulds.

[1][12] The south aisle shows a plain parapet above coursed ironstone with ashlar edgings reflecting the lower stages of the tower.

Three three-light windows, one plain glazed to the west of the porch, two stained to the east, are of same style to those of the north aisle, but with added facetted details between the head arches and the frames.

On the west and east side are flat headed windows with twin lights, clear glazing, and tracery, and hood moulds with personified label stops.

[1][12] The central chancel east window is of five lights, separated by transom; the ten segments rise to pointed arches with cinquefoils—lobes formed by the overlapping of five circles—and spandrels.

[1][12] The church is rendered throughout, with mid-19th-century plain wooden roofs supported by simple arch-braces, finished at their spring by carved stone corbel angels.

On the north wall is an early 19th-century painted Royal arms, quatrefoil framed, with added note of De Ligne Gregory, rector H. Dodwell, and Thomas Plaskett.

The tower interior is unrendered, and within it, at the south-west, is a pointed arch doorway with oak door leading to the upper stages.

At the lower part is a late 19th-century wooden rood screen of Perpendicular style, of three sections—voided in the centre section and void above with panelling below in the outer, and tracery above in all, the top line with crenellations.

The north chapel has mirrored a more elaborate tomb niche including spandrels containing angels holding shields, and a castellated top with foliate cross.

[1][12] The church Perpendicular (Pevsner) or Decorated (Cox) octagonal font is c.1400, although re-cut, and includes a carving of Christ holding a chalice.

One has an ogee-arched head with cinquefoil and bosses surmounted by a foliate cross, with square columns either side each topped with a crocketted pinnacle.

The third, of similar style, but topped by a knight's helmet and two coat of arms, is dedicated to George De Ligne Gregory (1 May 1740 - 24 August 1822).

Married Catherine, 3rd daughter of Robert Holden Esqu.of Nutthall Temple, Notts & died June 7th 1869 aged 85 & was buried at Bramcote.

"[15] The north aisle east stained glass window is dedicated, by brass plaque, to a Henry Hemsley (died 24 February 1888), and was erected by his neighbours and parishioners.

To the left, between this and the aisle central window, is a memorial with pointed head and apron below, containing two round-headed panels with scrolling and shell device above.

The left panel shows a dedication to "Arabella wife of Edward Saul, Clerk, a vertuous woman lovely in her life and lamented in her death.

Further down is that to "Edward Saul A. M. Prependary of Lincoln and from the year 1705, rector of this parish; to the memory of his wife and family, deserving all marks of respect and affection from him erected this monument 1744. and died September the 12th 1753, aged 77".

A further chancel stone floor slab, now badly worn, is noted by Turnor to be to the memory of James Morrison, cleric (died 1705, aged 33), and set by his "grieving widow", Eleanor.

Within the tower are two lozenge-shaped black-framed coat of arms funerary hatchments, one at the north, one at the south, each containing the motto "Resurgam" (I shall rise again), within a scroll.

John Usher of the Isle of Ely, 1701, and Edward Deligne Gent; Natives of Harlaxton gave each of them the sum of ten pounds; the interest to be distributed yearly to the blind, lame, aged, and impotent people, and poorer widows, of the said parish.