|Predecessor||Æthelmær, Bishop of Elmham|
|Successor||William de Beaufeu, Bishop of Thetford|
|Denomination||Roman Catholic Church|
|Monarch||William I of England|
|Preceded by||Office established|
Born in Normandy, Herfast joined William the Conqueror during the Norman Conquest of England and was appointed head of the royal writing office after the Battle of Hastings. He was Lord Chancellor of England from 1068 to 1070.
After serving as Lord Chancellor, he was consecrated Bishop of Elmham in 1070, but about 27 May 1072 he moved the see to Thetford, thus becoming Bishop of Thetford. He attempted to move his diocese to Bury St. Edmunds Abbey, with the assistance of Herman the Archdeacon, but the proposal was opposed by its abbot, Baldwin. Herfast finally lost in the King's Court in 1081 and was fined a crippling amount, which was unpaid when he died.
- Fryde, E. B.; Greenway, D. E.; Porter, S.; Roy, I. (1986). Handbook of British Chronology (3rd ed.). Cambridge: Cambridge University Press. p. 83. ISBN 0-521-56350-X.
- Fryde, E. B.; Greenway, D. E.; Porter, S.; Roy, I. (1986). Handbook of British Chronology (3rd ed.). Cambridge: Cambridge University Press. pp. 217 and 243. ISBN 0-521-56350-X.
- Licence, Tom (June 2009). "History and Hagiography in the Late Eleventh Century: The Life and Work of Herman the Archdeacon, Monk of Bury St Edmunds". English Historical Review. 124 (508): 518–521. ISSN 0013-8266.
- Greenway, Diana E. (1971). Fasti Ecclesiae Anglicanae 1066–1300. Vol. 2: Monastic cathedrals (northern and southern provinces). pp. 55–58.
- Williams, Ann (2000). The English and the Norman Conquest. Ipswich: Boydell Press. p. 46. ISBN 0-85115-708-4.
- Frank, Barlow (2004). "Herfast (d. 1084)". Oxford Dictionary of National Biography. Oxford University Press. doi:10.1093/ref:odnb/13075. ISBN 978-0-19-861412-8. (subscription or UK public library membership required)