"…Robertus de Quinci, Seierus de Quinci…" were the first two lay witnesses of the charter dated 1200 which records the foundation of Inchaffray Abbey by "Gilbertus filius Ferthead…comes de Stradern et…Matilidis filia Willelmi de Aubengni comitissa". "…Seier de Quinci…" subscribed the undated charter under which "Comes David frater regis Scottorum" founded Lindores Abbey. "Seerus de Quinci" confirmed the donation of "Davac Icthar Hathyn" made by "matris mea" to St Andrew´s priory by undated charter witnessed by "…Roberto de Quincy patre meo…Constant et Patricio filiis Nesii avi mei…".
He was created Earl of Winchester before 10 Feb 1207. "Seherus de Quency comes Wintonie" donated "ecclesiam de Gasc" to Inchaffray Abbey, for the souls of "patris nostri bone memorie Roberti de Quency et…matris nostre Orable et…Roberti de Quency primogeniti nostri et…Margarete uxoris nostre" by charter dated to [1210/13]. "Seherus de Quency comes Wintonie" donated "totam terram de Duglyn", held by "Nesus filius Willelmi avus meus" to Cambuskenneth priory, with the consent of "Robert filii mei", by undated charter.
He supported the barons against King John and was one of the 25 men chosen in Jun 1215 to enforce obedience of Magna Carta, being excommunicated by the Pope in Dec 1215. He went with Robert FitzWalter to invite Louis de France to England in early 1216, his lands being seized by King John as a consequence and granted to William Marshal, son of the Earl of Pembroke. He returned to the allegiance of King Henry III in Sep 1217 and his lands were restored to him 29 Sep 1217. "Saherus de Quinc[y] comes Wintonie" confirmed a donation of property "in territorio de Gask" to Inchaffray Abbey by charter dated to . "Seyerus de Quinci comes Wintonie" donated revenue from "molendino meo de Locres" to St Andrew´s priory, with the consent of "Rogeri filii et heredis mei", by undated charter, dated to [1217/18], witnessed by "Rogero de Quinci herede meo, Simone de Quinci persona de Louchres, Patricio filio Nesii…Simonis de Quinci".
He joined the Crusade in 1219 and died at the siege of Damietta. The necrology of Garendon abbey (Leicestershire) records that “dominus Saerus de Quyncy comes Wyntonie et Robertus filius Willielmi de Havercourt et Willielmus comes de Arundell” travelled to “Terram Sanctam” in 1219 and that Saher died on the journey “III Nov” and was buried “apud Acres”, his heart being burned and later buried at Garendon. The Annals of Dunstable record that “comes Wintoniæ” took the cross in 1219 but died, adding in a later passage that he died in 1220. The Annals of Dunstable record that “comes Wintoniæ” took the cross in 1219 but died, adding in a later passage that he died in 1220. Matthew Paris records the death in 1220 of “Saerus de Quinci comes Wintoniensis”. 1