The Gestis Comitum Barcinonensium names "Sancium" as son of "Raimirus filius Sancii Regis Navarrorum…ex…nobilissima domina de castro…Ayunarum". The Crónica de San Juan de la Peña names "Sancho et…García" as the two sons of King Ramiro and his wife "la filla del Comte de Bigorra nombrada Hermissenda et por baptismo Gelberda", stating in a later passage that Sancho was eighteen years old when he succeeded his father. "Sancii regis Ranimiri filio prolis Ermisende regina…Sanz Galinz tenente Boltania, Fertung Blasch cum suo fratre Galin Blasch, Guillermi Serui Dei" subscribed the charter dated 22 May 1035 [must be misdated] which records the donation of the churches of San Martín de Arasanz, San Pedro de Tou, San Felix y San Juan de Aínsa to Sobrarbe San Victorián made by Ramiro I King of Aragon. King Ramiro I donated the church of San Miguel "prope Calonica Baasa" to Sobrarbe San Victorián by charter dated 1035 [must be misdated], subscribed by "…Sancio Ranimiri regis filio primogenito, Sancio Ranimiri regis filio proles Ermesendis regina… ". The testament of King Ramiro I, dated 29 Jul 1059, bequeathed property to “filio meo Sancio filius Ermesendis...Sancio primogenito meo, Garsea filio meo, filia mea Taresa”, and to “domina mea Sancta Maria...super Sancte Cruçe filia mea Urraka”. The testament of King Ramiro I, dated 15 Mar 1061, bequeathed property to “Sancio filio meo filius Ermisindis qui vocata est per baptismum Gilberga...Aibar et Exabirri Iateri [ad] filio meo Sancio...filia mee Urraka cui est in Sancta Cruce...Garsea filio meo”.
He succeeded his father in 1063 as SANCHO I King of Aragon. Like his father, in the early years of his reign he did not use the title "king" but was referred to in documentation as "Sancius Ranimiro regis filius". From Jan 1072, he appears as "Sanctius gratia Dei Aragonense". He gained Barbastro from the Moors in 1064, although lost it the following year, and Alquezar in 1065. He was able to impose tribute on the Moors of Huesca, Tudela and Zaragoza, thereby greatly expanding Aragon's wealth. “Sancius...Rex filius Ranimiri Regis” donated property to Roda, for the salvation of “mea et uxoris ac filiorum”, by charter dated 18 Aug 1068, witnessed by “Sancio fratre suo de Rex Sancio, Garcia similiter, Senior Sancio Galim de Boltania, Senior Ato Galin in Abinzalla, Senior Fortung Belasch in santo Martino, suo fratre Galindo Belasch in Froceto, Senior Sancio Azenar in Petra-rubea, Guillermus servi Dei in Cabella...”.
After the murder of Sancho IV King of Navarre in 1076, he succeeded as SANCHO V King of Navarre. The precise circumstances under which the throne of Navarre passed to Sancho I King of Aragon have not been ascertained. The earliest (apparently reliably dated) charter so far identified which names Sancho as king of Navarre is dated Mar 1077: the dating clause of a charter dated Mar 1077, under which King Sancho I granted “kasas de Lope filio de donna Pura” to “Banzo Ezones de Biele”, records “ego Sancio Ranimirez...rex in Pampilona et in Aragona et in Superabi sive in Ripacorza...regnante rex Adefonsu in Castella...”. Evidently some difference persisted between Aragon and Castile about the succession in Navarre as the dating clause of a charter dated 14 May 1081, under which "domna Onneca" sold "media vinea in plano de Leiva" to “domno Iohanne”, records “regnante Aldefonsus rex in Legione et in Castella et in Pampilona...”. Aragon became the crossing point for pilgrims and merchants from France into Spain, Jaca in particular expanding into a city which was granted a charter of liberties in 1077 and became the Episcopal see. The death of al-Muqtadir of Zaragoza in 1081 was followed by a new wave of Aragonese conquests led by Sancho's eldest son Pedro. "Sancius…rex Aragonensium" granted privileges to the monastery of San Pedro de Siresa by charter dated 4 Sep 1082, the dating clause of which refers to "regnante rege Sancio cum uxore sua Felicia et filio suo Petro in Aragone et in Pamplona et in Superarbi sive in Ripacorza…domno Garsia fratre regis episcopo in Iaca…domno Sancio Ranimiri comite in Ripacorza, domna Sancia comitissa atque sorore regis presidente in Siresia…Raimundo Beringerii et Beringerii Raimundi fratribus comitibus in Barcelona". "Sancius rex Pampilonensium et Aragonensium…cum filio meo Petro" confirmed the rights of the bishop of Pamplona to the town of Pamplona by charter dated 28 Oct . Sancho I became the vassal of the Pope in 1088.
The Crónica de San Juan de la Peña records that King Sancho died at Huesca in 1094 and was buried in the "monasterio de San Iohan de la Peña". The "Corónicas" Navarras record that King Sancho was buried "en Mont aragón" but transferred to "Sant Johan de la Peyna por miedo de los moros". The Annales Compostellani record the death “pridie Non Jul” in 1094 of “Sancius Rex”. 1