The first church at Crosthwaite is believed to have been built in 553 AD under the direction of St Kentigern, who preached the Gospel in the area before moving on to Wales.

[3] In 1181 Jocelyn of Furness wrote of a new church at Crosthwaite recently built for Alice de Romilly, the Lady of Allerdale.

[3] During the 14th century (the historians of the church, Tom Wilson and J W Kaye estimate the date to have been about 1340) a chapel was added to the north side of the chancel, and later a south aisle.

In the early 16th century there were major changes to the building; the chancel arch was removed, a clerestory was added and existing side chapels were reconstructed.

[6] In 1909 the western end of the south aisle was converted into a baptistry to mark Hardwicke Rawnsley's 25 years of service as vicar.

There is a remarkable set of the ringers' rules dating from 1826, which is displayed in a large frame in the ringing chamber; they were penned by the English master from St Bees School.

[15][n 2] According to Wilson and Kaye the existence of the crosses shows that the church was consecrated "to the 'English use' (secundum consuetudinem)" and not according to Roman Catholic rite.

[15] In a 1960s guide John Betjeman drew attention to some of the above and to the finely carved 14th-century font, a number of 15th-century effigies, the reredos by the Keswick School of Industrial Art and the altar draped with a banner bearing the Greek motto "εν τούτῳ νίκα", meaning "in this sign you will conquer", a motto adopted by Constantine the Great and by the Knights Templar.

[17] The reredos incorporates three repoussé panels by Edith Rawnsley and John Birkett, who were also responsible for the hanging lights, the mosaics and the pulpit.

[18] Southey is depicted in marble, with one hand resting on his heart and the other on a book, with an epitaph by William Wordsworth; "Ye Vales and Hills, whose beauty hither drew/The poet's steps, and fixed him here, on you/His eyes have closed.