Reginald de Braose (died 1227) was the son of William de Braose, 4th Lord of Bramber and Matilda de St. Valery. He was a scion of the powerful Marcher family of Braose, and related by marriage to the Princes of Wales.

He supported his brother Giles in his rebellions against King John. They were both active against the King in the baron's war. Neither was present at the signing of Magna Carta because they were still rebels who refused to compromise. John acquiesced to Reginald's claims to the de Braose estates in Wales in May 1216. He became Lord of Brecon, Abergavenny, Builth and other Marcher Lordships but was very much a vassal of Llewelyn Fawr, Prince of Gwynedd who became his father-in-law in 1222 when Reginald married Llywelyn's daughter, Gwladys Ddu. Henry III restored Reginald to favour and the Bramber estates (confiscated from William by King John) in 1217. At this seeming betrayal, Rhys and Owain, Reginald's nephews who were princes of Deheubarth, were incensed and they took Builth (except the castle). Llywelyn Fawr also became angry and besieged Brecon. Reginald eventually surrendered to Llewelyn and gave up Seinhenydd (Swansea). By 1221 they were at war again with Llewelyn laying siege to Builth. The siege was relieved by Henry III's forces. From this time on Llewelyn tended to support the claims of Reginald's nephew John de Braose concerning the de Braose lands.

Reginald was a witness to the re-issue of Magna Carta by Henry III in 1225. He died two years later and was succeeded by his son, the ill-fated William de Braose, Lord of Abergavenny. His daughter Matilda was the wife of Rhys Mechyll, Prince of Deheubarth.