Father: John de Braose
Mother: Margaret (daughter of Llewelyn Fawr)

After his father's death, John remained in the care of his mother, who remarried to Walter de Clifford. He was afterwards associated with tenements which had previously been held by Cliffords at Culminton and Glasbury.

Complete Peerage states under John de Breuse of Glasbury, co. Brecon that

" He had disputes about this manor(on the borders of cos. Brecon and Radnor) with Roger de Clifford in 1272, and with John Giffard of Brimpsfield and Maud his wife. John and Maud conceded the manor to him and his heirs male in 1275, and Roger's claim was settled for 100 marks of silver. (Curia Regis, roll no. 205, mm. 5 d, 6 d, 15; Coram Rege, Mich. 3-4 Edw 1, m. 41, Mich. 4-5 Edw.
1, m. 17 Mich. 5-6 Edw. 1, m. 8)"

John Giffard's wife, Maud, was John of Glasbury's half-sister from his mother's second marriage.

John was an executor of the will of his cousin, Richard de Clare, Earl of Gloucester and Hertford, who died in 1262. He held lands from the Earls. In the inquest of Gilbert de Clare in 1295, John's widow, Margery was still holding dower lands in Bisseley, Glos.

The arms given are recorded in Walford's Roll, c1275 (John de Brusse), Charles' Roll, c1285 (W.... Breus) and St. George's Roll, c1285 (John de Brewase). He may have been a member of Richard de Clare's household, which could explain why his arms are a differenced version of the Clare arms.