Around 1120 a charter in Monmouth was signed by, among others, Geoffrey the scribe (Gaufridus scriba).
The signature of Geoffrey Arthur (Gaufridus Arturus) is found on five charters and deeds in Oxford between 1129 and 1150. One of them, a deed in 1139, Geoffrey signed as magister Gaufridus Arturus. Magister was a term for a teacher.
Copies of the History of the Kings of Britain (Historia regum Britanniae) name the author as Geoffrey of Monmouth (Galfridus Monemutensis) or Geoffrey Arthur of Monmouth (Galfridus Artur Monemutensis).
In 1151 Geoffrey signed charters as Geoffrey bishop-elect of St. Asaph’s (Gaufridus electus sancti Asaphi) and as Geoffrey bishop of St. Asaph’s (Gaufridus episcopus sancti Asaphi).
Being elected as a bishop meant Geoffrey had to become a priest. He was ordained on February 16th 1152 then was consecrated bishop of St. Asaph’s on February 22nd.
Geoffrey’s last surviving signature is on a major historical document: the Westminster Treaty which sealed the end of the English civil war called the Anarchy. The treaty settled that King Stephen would rule to his death, after which the crown would be passed to Henry, Duke of Anjou, the future Henry II.
Scholars have extrapolated parts of Geoffrey’s life from these signatures.
Geoffrey probably was born and grew up in Monmouth, a Welsh-English frontier town held by a Breton lord whose family had supported William the Conqueror.
Perhaps Geoffrey’s father was named Arthur. Some scholars claim that Arthur is a Breton name; the name Geoffrey is Breton. It was common during the years following the Conquest in 1066 for Breton and Norman and sometimes French knights to emigrate to Britain. Many of them married Anglo-Saxon women. Others, like Wihenoc, the Breton Lord of Monmouth, brought their wives with them.
Geoffrey could have studied Latin at the priory in Monmouth. He could have become a clerk which would explain his first known signature. If his parents had enough money or if he came to the attention of a well-off patron, a bright young clerk might be sent to the Chapel of St. George at Oxford Castle as a secular canon. That position would put him into contact with teachers, scholars, and churchmen. Most of his signatures are on documents also signed by Walter, the Archdeacon of St. George’s, as well as other canons of that Chapel.
Geoffrey’s superiors in Oxford were active in the affairs of the diocese of Lincoln. Lincoln was the largest diocese in England, and its Bishop was Alexander “the Magnificent.” Alexander loved grandeur and he was involved in the affairs of the state as well as the church. In addition, he was a patron of historians. Geoffrey dedicated his “Prophesies of Merlin” to Bishop Alexander of Lincoln.
It would be fitting to imagine that in his later years Geoffrey was elevated to Bishop of St. Asaph’s because of the great success of his writings. After all, the story of St. Asaph was tied to that of St. Kentigern who appeared in Geoffrey’s Life of Merlin (Vita Merlini).
The best source I’ve found for a total view of Geoffrey’s life and work is by Michael J. Curley. I used it for much of the information in this post.
Geoffrey of Monmouth by Michael J. Curley. 1994. Twayne Publishers, MacMillan Publishing Company, New York. Twayne’s English Author Series Number 509.