The earliest well-documented progenitor of this family was Robert Lord of Cemais, whose charter to the monks at Montacute from around 1121 names his parents, Martin and Geva.

Geva is known to have been the daughter and heiress of Serlo de Burci, bringing the lands of her father to her marriage, which included Low Ham, Pylle, and Hornblotton.

By her second marriage to William de Falaise, which had occurred by 1086, she was to pass to her son and heir, Robert, additional land in Devonshire.

He was a benefactor to various monasteries, giving land at Compton to Goldcilffe, the church of Blagdon to Stanley in Wiltshire, and the manor of Teignton to Montacute Priory in Somerset.

In 1134, he joined with other Norman lords in South Wales in resisting the sons of Gruffydd, and witnessed several charters of the Empress Maud, to whom he was adhered.

In 1198 he made an exchange of lands in Combe Martin, Devon, with Warin de Morcells, who had married his sister, Sibyl.

In 1222, while still underage, the King granted him licence to have a fair at his manor of Combe Martin in Devon, every year until he should come of age, which occurred before September 1231.

In 1271, the King's son, Edmund, gave him custody of the castles and counties of Carmarthen and Cardigan, and in 1278 he was one of the justices appointed to hear and determine complaints concerning the Bishop of St. David's in Wales.

Maud then married Geoffrey de Camville (died 1308), of Clifton Campville, Staffordshire, who had summons to attend the king at Portsmouth, with horse and arms, to embark in the expedition then proceeding to Gascony.

The barony of Barnstaple was recovered on Geoffrey's death by Maud's son William I Fitz Martin, who was aged 25 when he received livery of his inheritance 1 April 1282.

By this stage, junior branches of the family were already established in Waterston, Dorset (later of Athelhampton); St. David's, Wales; and by 1365 Thomas Martyn had settled in the town of Galway, Ireland.