Remaining correspondence of Tajo and bishop Braulio confirms that in the period before 651 (death of Braulio) Tajo was a presbyter in Saragossa, and then an abbot of a monastery (in or near Saragossa). After 651 he was elected as successor of Braulio to the see of Saragossa. He probably died in 683 and was succeeded by Valderedus (who subscribes the canons of 13th council of Toledo in 683 as a bishop of Saragossa).
In the letter to Quiricus, bishop of Barcelona,Tajo, already bishop of Saragossa, says that he has got a cognomen 'Samuel'. C. Lynch (1938: 60) supposed that Tajo could be a Goth converted from Arianism and Samuel would be his baptismal name, but he cannot be right as Catholics did not practice the rebaptism of Arians. The name 'Samuel' may rather indicate the Jewish origin. Moreover, the only extant manuscript of Braulio's letters, 9th c. codex preserved in León (ms. 22), is called on folio 1v. 'Samuel liber'. It led Lynch to believe that Tajo of Saragossa might have been the first editor of Braulio's letter collection (Lynch 1938: 201-202).