This important monk of the 8th century was possibly born and raised at Liébana, which was not far from Santander, Spain. He may have been from a poor family, considering the invectives written by a heretical archbishop about him.

Historically we first learn about Beatus in the year 776, at which time he wrote a 12-volume commentary on the Book of Revelation. Ten years later, the elderly archbishop of Toledo, Elipandus, began the revival of a form of the Nestorian heresy, in which he insisted that Jesus was only the adopted son of the eternal God. He preached this heresy all over Spain and drew many away from the Church. Beatus, who was a monk in the Asturian mountains at a place called Liébana, strove to counteract the heresy.

Etherius, the future bishop of Osma, joined Beatus in jointly writing a refutation of this heresy. Through Beatus writings and preaching many returned to the faith. When Elipandus became aware of this he was furious and wrote to Abbot Fidelis who was apparently a leader of great standing in that area. Elipandus' scathing letter attacked Beatus as an interfering vagrant mountaineer who had the impudence to set himself against the archbishop and the Church. He considered Etherius a young boy easily swayed by the ideas of this adventurous Beatus. He insisted that Beatus amend his ways or be delivered to the archbishop for correction.

When Abbot Fidelis showed the letter to him, Beatus, with the assistance of Etherius, responded by publishing a book, which laid out the orthodox teachings of the Church. Alcuin, a learned teacher of the times, praised him for his writings and described Beatus as a learned and very holy man.

Beatus was a teacher and adviser of Queen Adosinda of León. He wrote and reedited his Commentary on the Book of Revelation twice at her request. Perhaps of the greatest importance is not so much the text as the illuminated manuscripts which give us a view of the development of Spanish art, showing the Celtic and Coptic influence. Beatus is also credited with writing several hymns which were a part of the Mozarabic Spanish Liturgy.