Ranulf (Ralph) was the son of Ranulf de Briquessart, vicomte of the Bessin, and Matilda, daughter of Richard, vicomte of the Avranchin. He had two brothers, an older one, Richard, who died young, and a younger one, William (d. 1129×35), who married Cecily de Rumilly, daughter of Robert de Rumilly, with whom he had two sons and three daughters; Ranulf had one sister, Agnes, first wife of Robert de Grandmesnil (d. c. 1136). He is first recorded on 24 April 1089 and appears in 1093-94 with his uncle, Hugh d'Avranches, earl of Chester (d.1101). He married around 1098, Lucy (d.c.1138), heir of the honour of Bolinbroke, who had been married previously to Ivo Taillebois and Roger fitz Gerold. Ranulf's marriage to Lucy brought him extensive lands in Lincolnshire. He was for a time lord of Appelby (though Ivo Taillebois), and held lands in Carlisle, Cumberland and Westmorland. He founded Wetherhal Priory near Carlisle. Ranulf was frequently in Normandy and present regularly at the court of Henry I. He was appointed third earl of Chester in succession to his cousin, Richard, who had died in November 1120. With Lucy he had a son, Ranulf (II) de Gernon (d.1153), and a daughter, Alice, who married Richard de Clare (d.1136). He also had an illegitimate daughter, who married Richard Bacun, and an illegitimate son, Benedict. Fulk de Briquessart was possibly a nephew or another illegitimate son. Ranulf died in January 1129 and was buried in the chapter house of Chester Abbey.