He will have spent most of his life at Sempringham, despite the frequent modern assertion that he was a monk of Bourne Abbey.
This interpretation is supported by Mannyng's introduction to Handlyng Synne, in which he says that he had been at the abbey fifteen years: ten in the time of John Camelton (Hamilton) (the prior at Sempringham from c1298 to 1312), and five winters with Hamilton's successor, John Clyntone.
Handlyng Synne (1303) is a twelve thousand line devotional or penitential piece, written in Middle English rhymed couplets, deriving many of its exempla from the Anglo-Norman Manuel des Peches of William of Waddington.
Mannyng's Chronicle, supposedly completed in 1338, translates Wace's Roman de Brut for British history from the Anglo-Norman, before translating Piers Langtoft's (Peter of Langtoft) Chronicle for English and post-Conquest history.2 Mannyng was primarily a historiographer, and his significance lies in his participation in the tri-lingual tradition of writing history.
His work in Middle English is part of a larger movement at the beginning of the fourteenth century towards the replacement of Latin and Anglo-Norman by written works in Middle English, but is not groundbreaking.