St Pega's has a clerestoreyed nave with N and S aisles and W bell-cote, and a chancel with N chapel and vestry which together extend the N aisle to the E wall as the chancel. The nave is tall and narrow, with long-and-short quoins at the SW angle which suggest an 11thc. date. The N arcade dates from the 12thc., and the S arcade from the 13thc. The N chapel arch and the chancel arch are later 12thc, the latter perhaps in its lower parts only. The exterior is faced with ashlar blocks; regular in the S aisle, irregular elsewhere. Romanesque features are the nave doorways, the S elaborate and protected by a 14thc. porch, the N plain and unprotected; the N nave arcade, chancel arch and N chapel arch; the W bell-cote, and a loose capital now in the N aisle.

A confirmation of the grant of lands to Peterborough (Medeshamstede) by Wulfhere, king of Mercia, in 664 includes Peakirk, but this is generally thought to be a post-Conquest forgery. Like most of the Peterborough villages it does not appear in the Domesday Survey.

Benefice of Peakirk with Glinton and Northborough.

The dedication is unique. Pega was a sister of St Guthlac of Croyland and a member of the Mercian nobility who became an anchoress and died in 719 returning from a pilgrimage to Rome. The capital forms of the N arcade, including the zigzag scallops, also appear in the S arcade at nearby Maxey.