Tradition says Marwenne was one of the children of Brychan, king of the Christian kingdom of Brecknock in South Wales. Many of Brychan's large family became "saints", i.e. devoted missionaries, hermits and ascetics, they crossed the Severn Sea into Cornwall and even Brittany, where some of the Cornish Saints names reappear in the names of Breton parishes. Marwenne was the sister of St Nectan of Hartland, St Teath, St Tudy, St Endelienta, St Morwenna of Morwenstow and others. Some authorities consider the Marwenne and Morwenna are identical.
St Marwenne is thought to have established her hermitage on the site where the War Memorial now stands east of the church in Marham. She thus initiated the first ecclesiastical settlement in the village to which she gave her name.
The feast of St Marwenne falls on August 12th according to the Kalendar of the Celtic Church. the following Sunday is observed as Revel Sunday at Marham church, and the next day , the Monday following the feast, there takes place in the village the Marhamchurch Revel. A survival into modern tomes of a medieval feast. The Queen of the Revel, one of the school children of the village, elected by her fellows, is crowned by " Father Time" on the site of St Marwenne's hermitage; and there follows the Revel Procession around the village, led by the Queen riding on a white horse and followed by her attendants. the procession concludes at the Revel Field where festivities take place.